Synchronous induction motor and manufacturing method and drive unit for the same, and hermetic electric compressor

ABSTRACT

A synchronous induction motor features improved assemblability of a rotor, significantly reduced production cost, and improved operation performance of the motor. A plurality of die-cast secondary conductors is provided around a rotor yoke constituting the rotor of the synchronous induction motor. End rings are die-cast integrally with the secondary conductors on the peripheral portions of both end surfaces of the rotor yoke. Permanent magnets are inserted into slots formed such that they penetrate the rotor yoke. The openings of both ends of the slots are closed by a pair of end surface members formed of a non-magnetic constituent. One of the end surface members is secured to the rotor yoke by one of the end rings when the secondary conductors and the end rings are formed. The other end surface member is secured to the rotor yoke by a fixture.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a synchronous induction motorconstituted by a plurality of secondary conductors provided on theperipheral portion of a rotor yoke, an end ring which is positioned onthe peripheral portions of both end surfaces of the rotor yoke and whichis integrally formed with the secondary conductors by die casting, and apermanent magnet embedded in the rotor yoke.

[0003] 2. Description of the Related Art

[0004] Conventionally, an air conditioner or a refrigerator, forexample, incorporates a hermetic electric compressor for therefrigerating cycle of a cooling unit of the air conditioner or therefrigerator. As an electric constituent for driving the compressor, aninduction motor, a DC brushless motor, or a synchronous induction motordriven by a single-phase or three-phase commercial power supply has beenused.

[0005] The rotor of the synchronous induction motor is constituted by astator having stator windings and a rotor rotating in the stator. Aplurality of secondary conductors positioned around a rotor yoke thatmakes up the rotor are die-cast. Furthermore, end rings are integrallyformed with the secondary conductors by die-casting onto the peripheralportions of both end surfaces of the rotor yoke. Slots are formedthrough the rotor yoke, permanent magnets are inserted in the slots, andthe openings at both ends of the slots are respectively secured by endsurface members.

[0006] The permanent magnets to be provided in the rotor are inserted inthe slots formed in the rotor yoke, then secured by fixing members.Furthermore, in order to ensure good rotational balance of the rotor,balancers are installed in the vicinity of the end rings positioned onthe peripheral portions of the end surfaces of the rotor yoke. In thiscase, after forming the end rings by die casting, the end surfacemembers for fixing the permanent magnets in the slots and the balancersare separately installed. This has been posing a problem in that theassembling efficiency of the synchronous induction motor is considerablydeteriorated.

[0007] Furthermore, in order to secure the space for the slots forfixing the permanent magnets in the rotor, the end rings have to be madesmall. This inevitably leads to small sectional areas of the end rings.As a result, the heat generated by the rotor during operation increases,leading to a problem in that running performance is degraded due todegraded magnetic forces of the magnets, and, if rare earth type magnetsare used for the permanent magnets, then significant demagnetizationoccurs.

SUMMARY OF THE INVENTION

[0008] Accordingly, the present invention has been made with a viewtoward solving the problems with the prior art described above, and itis an object of the present invention to provide a synchronous inductionmotor that features improved assemblability of a rotor of a synchronousinduction motor and improved running performance.

[0009] According to one aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor rotating in the stator, a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting, end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting, permanent magnets inserted in slots formed such that theypenetrate the rotor yoke, and a pair of end surface members formed of anon-magnetic material that closes the openings of both ends of theslots, wherein one of the end surface members is secured to the rotoryoke by one of the end rings when the secondary conductors and end ringsare formed, and the other end surface member is secured to the rotoryoke by a fixture. Therefore, one of the end surface members can besecured to the rotor yoke at the same time when the secondary conductorsand the end rings are die-cast.

[0010] With this arrangement, after the permanent magnets are insertedinto the slots, the permanent magnets can be secured to the rotor merelyby securing the other end surface member to the rotor yoke by a fixture.It is therefore possible to reduce the number of steps for installingthe permanent magnets with resultant improved assemblability, permittingthe overall productivity of synchronous induction motors to bedramatically improved.

[0011] According to another aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor rotating in the stator, a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting, end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting, permanent magnets inserted in slots formed such that theypenetrate the rotor yoke, and a pair of end surface members formed of anon-magnetic material that closes the openings of both ends of theslots, wherein a non-magnetic member is disposed in contact with theinner sides of the two end rings to secure the two end surface membersby pressing them against the rotor yoke by the non-magnetic member. Itis therefore possible to increase the sectional areas of the end ringsby the amount provided by pressing the end surface members against thenon-magnetic member.

[0012] With this arrangement, the loss of the rotor can be decreased bythe amount equivalent to the increased portion of the sectional areas ofthe end rings. This allows the amount of generated heat of the rotor tobe reduced, making it possible to significantly improve the runningperformance of the synchronous induction motor.

[0013] According to yet another aspect of the present invention, thereis provided a synchronous induction motor having a stator equipped witha stator winding, a rotor rotating in the stator, a plurality ofsecondary conductors which is positioned around a rotor yokeconstituting the rotor and which is formed by die casting, end ringswhich are positioned on the peripheral portions of both end surfaces ofthe rotor yoke and which are integrally formed with the secondaryconductors by die casting, permanent magnets inserted in slots formedsuch that they penetrate the rotor yoke, and a pair of end surfacemembers formed of a non-magnetic material that closes the openings ofboth ends of the slots, wherein a balancer formed into a predeterminedshape beforehand is secured by a fixture to the rotor yoke together withthe end surface member. Therefore, the ease of installation of thebalancer can be considerably improved.

[0014] With this arrangement, it is no longer necessary to secure thepermanent magnets and the balancer separately, with consequent greaterease of installation. This permits dramatically improved productivity ofthe synchronous induction motor.

[0015] According to still another aspect of the present invention, thereis provided a synchronous induction motor having a stator equipped witha stator winding, a rotor rotating in the stator, a plurality ofsecondary conductors which is positioned around a rotor yokeconstituting the rotor and which is formed by die casting, end ringswhich are positioned on the peripheral portions of both end surfaces ofthe rotor yoke and which are integrally formed with the secondaryconductors by die casting, permanent magnets inserted in slots formedsuch that they penetrate the rotor yoke, and a pair of end surfacemembers formed of a non-magnetic material that closes the openings ofboth ends of the slots, wherein a plurality of laminated sheet balancersis secured by a fixture to the rotor yoke together with the end surfacemember. Therefore, the ease of installation of the balancer is improved,permitting dramatically improved productivity to be achieved.

[0016] Furthermore, since a plurality of sheet balancers is laminated,using inexpensive metal sheets for the balancer allows a considerablereduction in the cost of the balancer. This leads to a dramaticallyreduced production cost of the synchronous induction motor.

[0017] According to a further aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor rotating in the stator, a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting, end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting, permanent magnets inserted in slots formed such that theypenetrate the rotor yoke, and a pair of end surface members formed of anon-magnetic material that closes the openings of both ends of theslots, wherein at least one of the end surface members and a balancerare formed into one piece. Hence, the number of components can bereduced. This permits simpler installation of the end surface members,resulting in dramatically improved productivity.

[0018] According to another aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor rotating in the stator, a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting, end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting, permanent magnets inserted in slots formed such that theypenetrate the rotor yoke, a pair of end surface members formed of anon-magnetic material that closes the openings of both ends of theslots, and a balancer secured by being press-fitted to the inner side ofat least one of the end rings. Hence, the installation of the balancercan be simplified. This arrangement makes it possible to significantlyimprove the productivity of the synchronous induction motor.

[0019] According to another aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor rotating in the stator, a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting, end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting, permanent magnets inserted in slots formed such that theypenetrate the rotor yoke, and a pair of end surface members formed of anon-magnetic material that closes the openings of both ends of the slotsin which the permanent magnets have been inserted, wherein the two endsurface members are secured to the rotor yoke by the two end rings whenthe secondary conductors and the end rings are formed. This arrangementmakes it possible to obviate the need of, for example, the cumbersomestep for inserting the permanent magnets into the slots, then attachingthe end surface members to both ends of the rotor yoke after die-castingthe end rings, as in the case of a prior art. Thus, the productivity ofthe rotor can be dramatically improved.

[0020] According to a further aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor which is secured to a rotating shaft and whichrotates in the stator, a secondary conductor provided around the rotoryoke constituting the rotor, and a permanent magnet embedded in therotor yoke, wherein a magnetic field produced by the permanent magnetdoes not pass through the rotating shaft. Thus, it is possible toprevent the rotating shaft from being magnetized. This arrangement makesit possible to prevent iron powder or the like from adhering to therotating shaft and to protect the rotating shaft and a bearing frombeing worn due to the friction attributable to the magnetic force of thepermanent magnet. This permits secure prevention of damage to the motorcaused by the friction.

[0021] According to a further aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor which is secured to a rotating shaft and whichrotates in the stator, a secondary conductor provided around the rotoryoke constituting the rotor, and a permanent magnet embedded in therotor yoke, wherein a magnetic field produced by the permanent magnetbypasses the rotating shaft. Thus, it is possible to prevent therotating shaft from being magnetized. This arrangement makes it possibleto prevent iron powder or the like from adhering to the rotating shaftand to protect the rotating shaft and a bearing from being worn due tothe friction attributable to the magnetic force of the permanent magnet.This permits secure prevention of damage to the motor caused by thefriction.

[0022] According to another aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor which is secured to a rotating shaft and whichrotates in the stator, a secondary conductor provided around the rotoryoke constituting the rotor, and a permanent magnet embedded in therotor yoke, wherein a magnetic field produced by the permanent magnetpasses through only the rotor yoke, excluding the rotating shaft. Thus,it is possible to prevent the rotating shaft from being magnetized. Thisarrangement makes it possible to prevent iron powder or the like fromadhering to the rotating shaft and to protect the rotating shaft and abearing from being worn due to the friction attributable to the magneticforce of the permanent magnet. This permits secure prevention of damageto the motor caused by the friction.

[0023] In a preferred form of the synchronous induction motor inaccordance with the present invention, a void is formed in the rotoryoke between the permanent magnet and the rotating shaft, so that thepassage of the magnetic field produced by the permanent magnet can bereduced. Thus, it is possible to prevent the rotating shaft from beingmagnetized. This arrangement makes it possible to prevent iron powder orthe like from adhering to the rotating shaft and to protect the rotatingshaft and a bearing from being worn due to the friction attributable tothe magnetic force of the permanent magnet. This permits secureprevention of damage to the motor caused by the friction.

[0024] In another preferred form of the synchronous induction motor inaccordance with the present invention, a pair of the permanent magnetsis disposed with the rotating shaft therebetween, and permanent magnetsfor attracting the magnetic field produced by the paired permanentmagnets are disposed at both ends of a line that passes the pairedpermanent magnets and the rotating shaft. It is therefore possible toprevent the magnetic field produced by the paired permanent magnets frompassing through the rotating shaft. Thus, it is possible to prevent therotating shaft from being magnetized. This arrangement makes it possibleto prevent iron powder or the like from adhering to the rotating shaftand to protect the rotating shaft and a bearing from being worn due tothe friction attributable to the magnetic force of the permanent magnet.This permits secure prevention of damage to the motor caused by thefriction.

[0025] In yet another preferred form of the synchronous induction motorin accordance with the present invention, the permanent magnets areprovided at both ends of a line that connects two magnetic poles, andthe permanent magnets are radially disposed substantially about therotating shaft. Hence, the magnetic field produced by the permanentmagnets can be spaced away from the rotating shaft. Thus, it is possibleto prevent the rotating shaft from being magnetized. This arrangementmakes it possible to prevent iron powder or the like from adhering tothe rotating shaft and to protect the rotating shaft and a bearing frombeing worn due to the friction attributable to the magnetic force of thepermanent magnet. This permits secure prevention of wear on the rotorcaused by the friction.

[0026] According to another aspect of the present invention, there isprovided a synchronous induction motor having a stator equipped with astator winding, a rotor rotating in the stator, a secondary conductorprovided around the rotor yoke constituting the rotor, and a permanentmagnet embedded in the rotor yoke, wherein the permanent magnet ismagnetized by current passed through the stator winding. Hence, forexample, a rotor in which a magnetic material for the permanent magnetthat has not yet been magnetized has been inserted is installed in thestator, so that the rotor can be inserted into the stator without beingmagnetically attracted to its surrounding. This arrangement makes itpossible to prevent inconvenience of lower productivity of thesynchronous induction motor, thus permitting improved assemblability ofthe synchronous induction motor. This allows a synchronous inductionmotor with high reliability to be provided.

[0027] In a preferred form of the synchronous induction motor inaccordance with the present invention, the permanent magnet is made of arare earth type magnet or a ferrite magnet, so that high magnetcharacteristic can be achieved. With this arrangement, the magnitude ofthe current passed through the stator winding can be reduced so as tocontrol the temperature at the time of magnetization to a minimum.Hence, the deformation of the rotor or the stator or the like that wouldbe caused by high temperature can be minimized, making it possible toprovide a synchronous induction motor with secured high quality.

[0028] Especially in the case of a synchronous induction motor, currentpasses through the secondary conductor even during normal synchronousoperation, causing the temperature of the entire rotor to rise.Therefore, the demagnetization at high temperature can be restrained byusing, for example, a ferrite magnet or a rare earth type magnet (thecoercive force at normal temperature being 1350 to 2150 kA/m and thecoercive force temperature coefficient being −0.7%/° C. or less).

[0029] In a preferred form of the synchronous induction motor inaccordance with the present invention, the stator winding is of asingle-phase configuration and has a primary winding and an auxiliarywinding, and the permanent magnet is magnetized by the current passedthrough either the primary winding or the auxiliary winding. Hence, itis possible to achieve better magnetizing performance than, for example,in the case where current is passed through both the primary winding andthe auxiliary winding at the same time. This allows an unmagnetizedmagnet material to be intensely magnetized.

[0030] In a preferred form of the synchronous induction motor inaccordance with the present invention, the stator winding is of athree-phase configuration that includes a three-phase winding. Thepermanent magnet is magnetized by current passed through a single phase,two phases, or three phases of the stator windings. Therefore, it ispossible to select the phase or phases through which current is to bepassed according to the disposition of the magnet or the permissiblecurrent (against deformation or the like) of the windings.

[0031] In yet another preferred form of the synchronous induction motorin accordance with the present invention, the stator windings are coatedwith varnish or a sticking agent that is heated to fuse the windings.Hence, for example, even if the stator windings generate heat and becomehot when an unmagnetized magnet material inserted into the rotor ismagnetized by passing current through the stator windings, it ispossible to restrain the deformation of winding ends of the statorwindings and the deterioration of winding films caused by the heat.Thus, since the winding ends of the stator windings do not deform evenif an unmagnetized magnet material inserted into the rotor ismagnetized, a highly reliable synchronous induction motor can beprovided.

[0032] Furthermore, the synchronous induction motor in accordance withthe present invention is installed in a compressor, allowing theproduction cost of the compressor to be considerably reduced.

[0033] Moreover, the compressor incorporating the synchronous inductionmotor in accordance with the present invention is used with an airconditioner or an electric refrigerator or the like. Hence, theproduction cost of the air conditioner or the electric refrigerator canbe significantly decreased.

[0034] According to another aspect of the present invention, there isprovided a manufacturing method for a synchronous induction motor havinga stator equipped with a stator winding, a rotor rotating in the stator,a secondary conductor provided around a rotor yoke constituting therotor, and a permanent magnet embedded in the rotor yoke, wherein amagnet constituent for the permanent magnet is embedded in the rotoryoke and current is passed through the stator winding to magnetize themagnet constituent. Hence, the rotor can be inserted into the statorwithout being magnetically attracted to its surrounding, permittingdramatically improved assemblability of the synchronous induction motor.This makes it possible to prevent an inconvenience of reducedproductivity of the synchronous induction motor, which permits improvedassemblability of the synchronous induction motor. As a result, a highlyreliable synchronous induction motor can be provided.

[0035] In a preferred form of the manufacturing method for thesynchronous induction motor in accordance with the present invention, arare earth type or ferrite material is used for the magnet constituent.Therefore, a high magnet characteristic can be achieved even if, forexample, a magnetizing magnetic field is weak. This makes it possible toreduce the current passing through the stator winding so as to minimizea temperature rise that occurs at the time of magnetization. Thus, thedeformation of the rotor or the stator or the like caused by hightemperature can be minimized, ensuring high quality of the synchronousinduction motor.

[0036] In a preferred form of the manufacturing method for thesynchronous induction motor in accordance with the present invention,the stator winding is of a single-phase configuration and has a primarywinding and an auxiliary winding, and the magnet constituent ismagnetized by the current passed through either the primary winding orthe auxiliary winding. Hence, it is possible to achieve bettermagnetizing performance than, for example, in the case where current ispassed through both the primary winding and the auxiliary winding at thesame time. This allows an unmagnetized magnet material to be intenselymagnetized.

[0037] In a preferred form of the manufacturing method for thesynchronous induction motor in accordance with the present invention,the stator winding is of a three-phase configuration that includes athree-phase winding. The magnet constituent is magnetized by currentpassed through a single phase, two phases, or three phases of the statorwindings. Therefore, it is possible to select the phase or phasesthrough which current is to be passed according to the disposition ofthe magnet or the permissible current (against deformation or the like)of the windings.

[0038] In yet another preferred form of the manufacturing method for thesynchronous induction motor in accordance with the present invention,the stator windings are coated with varnish or a sticking agent that isheated to fuse the windings. Hence, for example, even if the statorwindings are subjected to electromagnetic forces when an unmagnetizedmagnet constituent inserted into the rotor is magnetized by passingcurrent through the stator windings, it is possible to restrain thedeformation of windings and the deterioration of the films of thewindings. Thus, since the winding ends of the stator windings do notdeform even if an unmagnetized magnet material inserted into the rotoris magnetized, a highly reliable synchronous induction motor can beprovided.

[0039] According to yet another aspect of the present invention, thereis provided a drive unit for a synchronous induction motor that includesa stator equipped with a stator winding formed of a primary winding andan auxiliary winding, a rotor rotating in the stator, a secondaryconductor provided around a rotor yoke constituting the rotor, apermanent magnet embedded in the rotor yoke, an operating capacitorconnected to the auxiliary winding, and a series circuit of a start-upcapacitor and a PTC, which is connected in parallel to the operatingcapacitor. This arrangement permits larger running torque to be providedat starting up the synchronous induction motor equipped with theoperating capacitor connected to the auxiliary winding, and the seriescircuit of the start-up capacitor and the PTC, which is connected inparallel to the operating capacitor. This enables the power consumedduring normal operation to be reduced, making it possible to provide adrive unit capable of running the synchronous induction motor withextremely high efficiency. Hence, considerably higher efficiency can beachieved during the operation of the synchronous induction motor.

[0040] According to still another aspect of the present invention, thereis provided a drive unit for a synchronous induction motor that includesa stator equipped with a stator winding formed of a primary winding andan auxiliary winding, a rotor rotating in the stator, a secondaryconductor provided around a rotor yoke constituting the rotor, apermanent magnet embedded in the rotor yoke, an operating capacitorconnected to the auxiliary winding, and a PTC connected in parallel tothe operating capacitor. This arrangement permits larger running torqueto be provided at starting up the synchronous induction motor equippedwith the operating capacitor connected to the auxiliary winding and thePTC connected in parallel to the operating capacitor. This enables thepower consumed during normal operation to be reduced, making it possibleto provide a drive unit capable of running the synchronous inductionmotor with extremely high efficiency. Hence, considerably higherefficiency can be achieved during the operation of the synchronousinduction motor.

[0041] According to yet another aspect of the present invention, thereis provided a drive unit for a synchronous induction motor that includesa stator equipped with a stator winding formed of a primary winding andan auxiliary winding, a rotor rotating in the stator, a secondaryconductor provided around a rotor yoke constituting the rotor, apermanent magnet embedded in the rotor yoke, an operating capacitorconnected to the auxiliary winding, and a series circuit of a start-upcapacitor and a start-up relay contact connected in parallel to theoperating capacitor. This arrangement permits larger running torque tobe provided at starting up the synchronous induction motor equipped withthe operating capacitor connected to the auxiliary winding, and theseries circuit of the start-up capacitor and the start-up relay contactconnected in parallel to the operating capacitor. This enables the powerconsumed during normal operation to be reduced, making it possible toprovide a drive unit capable of running the synchronous induction motorwith extremely high efficiency. Hence, considerably higher efficiencycan be achieved during the operation of the synchronous induction motor.

[0042] According to a further aspect of the present invention, there isprovided a drive unit for a synchronous induction motor that includes astator equipped with a stator winding formed of a primary winding and anauxiliary winding, a rotor rotating in the stator, a secondary conductorprovided around a rotor yoke constituting the rotor, a permanent magnetembedded in the rotor yoke, and an operating capacitor connected to theauxiliary winding. This arrangement permits larger running torque to beprovided at starting up the synchronous induction motor equipped withthe operating capacitor connected to the auxiliary winding. This enablesthe power consumed during normal operation to be reduced, making itpossible to provide a drive unit capable of running the synchronousinduction motor with extremely high efficiency. Hence, considerablyhigher efficiency can be achieved during the operation of thesynchronous induction motor.

[0043] According to a further aspect of the present invention, there isprovided a hermetic electric compressor having a compression unit and anelectric unit for driving the compression unit in a hermetic vessel,wherein the electric unit is secured to the hermetic vessel andconstituted by a stator equipped with a stator winding and a rotorrotating in the stator, the rotor has a secondary conductor providedaround a rotor yoke and a permanent magnet embedded in the rotor yoke,and a thermal protector for cutting off the supply of current to theelectric unit in response to a predetermined temperature rise isprovided in the hermetic vessel. Therefore, installing the thermalprotector onto the stator winding, for example, makes it possible to cutoff the supply of current to the electric unit if the temperature of thestator winding rises. This arrangement makes it possible to prevent thepermanent magnet embedded in the rotor yoke from being thermallydemagnetized by a rise in temperature of the electric unit. Hence, thesupply of current to the stator winding can be cut off before the statorwinding generates abnormal heat while the hermetic electric compressoris in operation. This makes it possible to securely prevent damage tothe stator winding and thermal demagnetization of the permanent magnetso as to ideally maintain the driving force of a synchronous inductionmotor, permitting significantly improved reliability of the electricunit.

[0044] According to a further aspect of the present invention, there isprovided a hermetic electric compressor having a compression unit and anelectric unit for driving the compression unit in a hermetic vessel,wherein the electric unit is secured to the hermetic vessel andconstituted by a stator equipped with a stator winding and a rotorrotating in the stator, the rotor has a secondary conductor providedaround a rotor yoke and a permanent magnet embedded in the rotor yoke,and a thermal protector for cutting off the supply of current to theelectric unit at a predetermined temperature rise is provided on theouter surface of the hermetic vessel. Therefore, it is possible to cutoff the supply of current to the electric unit if the temperature of theouter surface of the hermetic vessel rises due to the heat generated bythe electric unit. Thus, a temperature rise in the hermetic vessel canbe restrained, so that an accident, such as a fire, caused by atemperature rise in the hermetic vessel can be prevented.

[0045] In a preferred form of the hermetic electric compressor inaccordance with the present invention, the thermal protector isconstructed of a thermistor whose resistance value varies withtemperature and a controller that controls the supply of current to theelectric unit according to a change in the resistance value of thethermistor. Thus, if, for example, the temperature of the hermeticelectric compressor rises and exceeds a preset level, the controllercontrols the supply of current to the electric unit and cuts off thesupply of current to the electric unit. With this arrangement, it ispossible to control the current supplied to the stator winding beforethe hermetic electric compressor is run under overload and damaged. Thismeans that a temperature rise in the electric unit can be securelycontrolled by controlling the revolution of the electric unit, enablingthe service life of the electric unit to be prolonged, with resultantdramatically improved reliability of the hermetic electric compressor.

[0046] In a preferred form of the hermetic electric compressor inaccordance with the present invention, the thermal protector isconstituted by a bimetal switch, so that the current supplied to theelectric unit can be cut off also if the temperature of the hermeticelectric compressor rises. This obviates the need for controllablyadjust the electric unit by using an expensive circuit device, making itpossible to effect inexpensive and secure protection of the hermeticelectric compressor from damage caused by a temperature rise.

[0047] In a preferred form of the hermetic electric compressor inaccordance with the present invention, the thermal protector isconstituted by a thermostat that opens/closes a contact according totemperature, so that the current supplied to the electric unit can becut off also if the temperature of the hermetic electric compressorrises. This obviates the need for controllably adjusting the electricunit by using an expensive circuit device, making it possible to effectinexpensive and secure protection of the hermetic electric compressorfrom damage caused by a temperature rise.

[0048] According to a further aspect of the present invention, there isprovided a hermetic electric compressor having a compression unit and anelectric unit for driving the compression unit in a hermetic vessel,wherein the electric unit is secured to the hermetic vessel andconstituted by a stator equipped with a stator winding and a rotorrotating in the stator, the rotor has a secondary conductor providedaround a rotor yoke and a permanent magnet embedded in the rotor yoke,and an overload protector for cutting off the supply of current to theelectric unit in response to a predetermined overload current isprovided. Therefore, it is possible to cut off the supply of current tothe electric unit if the hermetic electric compressor is overloadedduring operation, thereby allowing the electric unit to be protectedfrom a temperature rise. Thus, damage to the electric unit can beprevented, enabling the service life of the electric unit to beconsiderably prolonged, with resultant dramatically improved reliabilityof the hermetic electric compressor.

[0049] In a preferred form of the hermetic electric compressor inaccordance with the present invention, the overload protector isconstituted by an overload switch, so that the current supplied to theelectric unit can be cut off to prevent a temperature rise in theelectric unit thereby to protect it if the hermetic electric compressoris overloaded during operation. Thus, damage to the electric unit can beprevented, enabling the service life of the electric unit to beconsiderably prolonged, with resultant dramatically improved reliabilityof the hermetic electric compressor.

[0050] In another preferred form of the hermetic electric compressor inaccordance with the present invention, the overload protector isconstituted by a current transformer for detecting the current suppliedto the electric unit and a controller for controlling the supply ofcurrent to the electric unit on the basis of an output of the currenttransformer, so that the current supplied to the electric unit can becut off by the controller if the hermetic electric compressor isoverloaded during operation. This arrangement makes it possible toprevent a temperature rise in the electric unit so as to protect theelectric unit. Hence, damage to the electric unit attributable to anoverload current can be securely prevented.

[0051] In another preferred form of the hermetic electric compressor inaccordance with the present invention, the controller cuts off thesupply of current to the electric unit after a predetermined timeelapses since a temperature or current exceeded a predetermined value.It is therefore possible to protect, by the controller, the electricunit which would be damaged if continuously subjected to an excessivetemperature rise or overcurrent caused by an overloaded operation or thelike of the hermetic electric compressor. Thus, damage to the electricunit can be prevented, enabling the service life of the electric unit tobe considerably prolonged, with resultant dramatically improvedreliability of the hermetic electric compressor.

[0052] In a further preferred form of the hermetic electric compressorin accordance with the present invention, the controller restarts thesupply of current to the electric unit after waiting for the elapse of apredetermined delay time since the supply of current to the electricunit was cut off. This means that the delay time is always allowedbefore the supply of current to the electric unit is restarted after thesupply of current to the electric unit was cut off. It is thereforepossible to prevent the rotor from becoming hot due to, for example,frequent repetition of energizing and de-energizing of the electricunit. Hence, demagnetization of the permanent magnet embedded in therotor due to heat can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 is a longitudinal sectional side view of a hermeticelectric compressor to which a synchronous induction motor in accordancewith the present invention has been applied;

[0054]FIG. 2 is a plan view of the hermetic electric compressor with itshermetic vessel split into two;

[0055]FIG. 3 is a cross sectional top view of the motor;

[0056]FIG. 4 is a partially cutaway cross sectional top view of a rotor;

[0057]FIG. 5 is a side view of the rotor;

[0058]FIG. 6 is a top view of the rotor;

[0059]FIG. 7 is a longitudinal side view of the rotor shown in FIG. 6;

[0060]FIG. 8 is a refrigerant circuit diagram of an air conditioner oran electric refrigerator or the like that uses the hermetic electriccompressor provided with the synchronous induction motor in accordancewith the present invention;

[0061]FIG. 9 is an electric circuit diagram of the synchronous inductionmotor;

[0062]FIG. 10 is a top view of another rotor;

[0063]FIG. 11 is a partially longitudinal sectional side view of therotor shown in FIG. 10;

[0064]FIG. 12 is a top view of another rotor;

[0065]FIG. 13 is a longitudinal sectional side view of the rotor shownin FIG. 12;

[0066]FIG. 14 is a top view of a rotor illustrating an end surfacemember that is provided inside an end ring and fixed by a balancer;

[0067]FIG. 15 is a diagram showing a part of the longitudinal sectionalside view of the rotor shown in FIG. 12;

[0068]FIG. 16 is a diagram showing a part of the longitudinal sectionalside view of a rotor incorporating a balancer formed of a plurality oflaminated sheet balancers;

[0069]FIG. 17 is a top view of a rotor in which an end surface memberand a balancer have been integrally formed and installed;

[0070]FIG. 18 is a diagram showing a part of the longitudinal sectionalside view of the rotor shown in FIG. 17;

[0071]FIG. 19 is a top view of another rotor;

[0072]FIG. 20 is a partial longitudinal sectional side view of the rotorshown in FIG. 19;

[0073]FIG. 21 is a top view of a rotor in which an end surface member isintegrally formed with a balancer and fixed to a rotor yoke;

[0074]FIG. 22 is a partial longitudinal sectional side view of the rotorshown in FIG. 21;

[0075]FIG. 23 is a cross sectional top view of another rotor;

[0076]FIG. 24 is an analytical diagram of a magnetic field of a rotor inthe layout of the permanent magnet shown in FIG. 4;

[0077]FIG. 25 illustrates a magnetic flux density in a rotating shaft ofthe rotor shown in FIG. 24;

[0078]FIG. 26 is an analytical diagram of a magnetic field of a rotorobserved when a void is formed in the rotor yoke in the layout of thepermanent magnet shown in FIG. 4;

[0079]FIG. 27 is a diagram illustrating a magnetic flux density in therotating shaft of the rotor shown in FIG. 26;

[0080]FIG. 28 is an analytical diagram of the magnetic field of therotor observed when a plurality of voids is formed in the rotor yoke inthe layout of the permanent magnet shown in FIG. 4;

[0081]FIG. 29 is a diagram illustrating a magnetic flux density in therotating shaft of the rotor shown in FIG. 28;

[0082]FIG. 30 is an analytical diagram of the magnetic field of a rotorconfigured such that a magnetic field produced by a permanent magnetbypasses a rotating shaft;

[0083]FIG. 31 is a diagram illustrating a magnetic flux density in therotating shaft of the rotor shown in FIG. 28;

[0084]FIG. 32 is a cross sectional top view of a rotor illustratinganother layout example of a permanent magnet;

[0085]FIG. 33 is a cross sectional top view of a rotor illustrating yetanother layout example of a permanent magnet;

[0086]FIG. 34 is a cross sectional top view of a rotor illustratingstill another layout example of a permanent magnet;

[0087]FIG. 35 is a cross sectional top view of a rotor illustrating afurther layout example of a permanent magnet;

[0088]FIG. 36 is a cross sectional top view of a rotor illustratinganother layout example of a permanent magnet;

[0089]FIG. 37 is a cross sectional top view of a rotor illustratinganother layout example of a permanent magnet;

[0090]FIG. 38 is a partially cutaway cross sectional top view of anotherrotor;

[0091]FIG. 39 is a partial longitudinal sectional side view of the rotorshown in FIG. 38;

[0092]FIG. 40 is a cross sectional top view of the rotor shown in FIG.38;

[0093]FIG. 41 is a cross sectional top view of another rotor;

[0094]FIG. 42 is a cross sectional top view of yet another rotor;

[0095]FIG. 43 is a cross sectional top view of still another rotor;

[0096]FIG. 44 is a cross sectional top view of a further rotor;

[0097]FIG. 45 is a cross sectional top view of another rotor;

[0098]FIG. 46 is an electrical circuit diagram of a three-phase,two-pole synchronous induction motor;

[0099]FIG. 47 is an electrical circuit diagram of a drive unit of thesynchronous induction motor in accordance with the present invention;

[0100]FIG. 48 is an electrical circuit diagram of a drive unit ofanother synchronous induction motor;

[0101]FIG. 49 is an electrical circuit diagram of a drive unit of stillanother synchronous induction motor;

[0102]FIG. 50 is an electrical circuit diagram of a drive unit of yetanother synchronous induction motor;

[0103]FIG. 51 is a diagram illustrating a relationship between arotational torque and a number of revolutions provided by each electriccircuit of each drive unit;

[0104]FIG. 52 is another refrigerant circuit diagram of an airconditioner or an electric refrigerator or the like that uses thehermetic electric compressor incorporating a synchronous inductionmotor;

[0105]FIG. 53 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of the hermetic electric compressor inaccordance with the present invention;

[0106]FIG. 54 is an electrical circuit diagram of a synchronousinduction motor;

[0107]FIG. 55 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of another hermetic electric compressor;

[0108]FIG. 56 is an electrical circuit diagram of a synchronousinduction motor of the hermetic electric compressor shown in FIG. 55;

[0109]FIG. 57 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of another hermetic electric compressor;

[0110]FIG. 58 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of still another hermetic electric compressor;

[0111]FIG. 59 is an electrical circuit diagram of a synchronousinduction motor of the hermetic electric compressor shown in FIG. 58;

[0112]FIG. 60 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of yet another hermetic electric compressor;

[0113]FIG. 61 is an electrical circuit diagram of a synchronousinduction motor of the hermetic electric compressor shown in FIG. 60;

[0114]FIG. 62 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of a further hermetic electric compressor;

[0115]FIG. 63 is an electrical circuit diagram of a synchronousinduction motor of the hermetic electric compressor shown in FIG. 62;

[0116]FIG. 64 is a longitudinal sectional side view of a part (in thevicinity of an end cap) of another hermetic electric compressor;

[0117]FIG. 65 is an electrical circuit diagram of a synchronousinduction motor of the hermetic electric compressor shown in FIG. 64;and

[0118]FIG. 66 is an electrical circuit diagram of a synchronousinduction motor of another hermetic electric compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] Embodiments of the present invention will be described in detailwith reference to the accompanying drawings. FIG. 1 is a longitudinalsectional side diagram of a hermetic electric compressor C, anembodiment to which the present invention is applied. A hermetic vessel1 in FIG. 1 includes a synchronous induction motor 2 in accordance withthe present invention in an upper compartment and a compressor 3 in alower compartment in the hermetic vessel 1, the compressor 3 beingrotatively driven by the synchronous induction motor 2. The hermeticvessel 1 is split into two parts in advance to house the synchronousinduction motor 2 and the compressor 3, then hermetically sealed byhigh-frequency welding or the like. The hermetic electric compressor Cmay be a rotary, reciprocal, scroll compressor, or the like.

[0120] The synchronous induction motor 2 is constructed of asingle-phase, two-pole stator 4 secured to the inner wall of thehermetic vessel 1 and a rotor 5 which is located on the inner side ofthe stator 4 and rotatively supported around a rotating shaft 6. Thestator 4 is provided with a stator winding 7 for applying a rotationalmagnetic field to the rotor 5.

[0121] The compressor 3 has a first rotary cylinder 9 and a secondrotary cylinder 10 separated by a partitioner 8. The cylinders 9 and 10have eccentric members 11 and 12 rotatively driven by the rotating shaft6. The eccentric positions of the eccentric members 11 and 12 arephase-shifted from each other 180 degrees.

[0122] A first roller 13 located in the cylinder 9 and a second roller14 located in the cylinder 10 rotate in the cylinders as the eccentricmembers 11 and 12 rotate. Reference numerals 15 and 16 denote a firstframe member and a second frame member, respectively. The first framemember 15 forms a closed compression space of the cylinder 9 betweenitself and the partitioner 8. Similarly, the second frame member 16forms a closed compression space of the cylinder 10 between itself andthe partitioner 8. The first frame member 15 and the second frame member16 are equipped with bearings 17 and 18, respectively, that rotativelysupport the bottom of the rotating shaft 6.

[0123] Discharge mufflers 19 and 20 are installed so as to cover thefirst frame member 15 and the second frame member 16. The cylinder 9 andthe discharge muffler 19 are in communication through a dischargeaperture (not shown) provided in the first frame member 15. Similarly,the cylinder 10 and the discharge muffler 20 are also in communicationthrough a discharge aperture (not shown) provided in the second framemember 16. A bypass pipe 21 provided outside the hermetic vessel 1, andis in communication with the interior of the discharge muffler 20.

[0124] A discharge pipe 22 is provided at the top of the hermetic vessel1. Suction pipes 23 and 24 are connected to the cylinders 9 and 10,respectively. A hermetic terminal 25 supplies electric power to thestator winding 7 of the stator 4 from outside the hermetic vessel 1 (thelead wire connecting the hermetic terminal 25 and the stator winding 7being not shown).

[0125] A rotor iron core 26 is formed of a plurality of laminatedrotator iron plates, each of which is made by punching anelectromagnetic steel plate having a thickness of 0.3 mm to 0.7 mm (notshown) into a predetermined shape. The laminated rotator iron plates arecrimped into one piece, or may be welded into one piece. End surfacemembers 66 and 67 are attached to the top and bottom ends of the rotoriron core 26. The end surface members 66 and 67 are formed of planesmade of a non-magnetic material, such as stainless steel, aluminum,copper, or brass. If the end surface members 66 and 67 should use amagnetic material, then the end surface members 66 and 67 would providea magnetic path, and the magnet of the rotor 5 would develop a magneticshort circuit, leading to degraded running performance of thesynchronous induction motor 2. For this reason, a non-magnetic materialis used for the members 66 and 67.

[0126]FIG. 2 is a plan view of the hermetic electric compressor C havingthe hermetic vessel 1 split into two parts. FIG. 3 is a cross sectionaltop view of the hermetic electric compressor C, FIG. 4 is a crosssectional top view of the rotor 5, and FIG. 5 is a side view of therotor 5. The stator 4 has the stator winding 7 wound around the stator4. A leader line 50 connected to the stator winding 7 and a coil end ofthe stator winding 7 are joined together with a polyester thread 70, andthe leader line 50 is connected to the hermetic terminal 25.

[0127] The rotor 5 is constructed of a rotor yoke 5A, die-castsquirrel-cage secondary conductors 5B positioned around the rotor yoke5A, a die-cast end ring 69 which is positioned on the peripheral portionof an end surface of the rotor yoke 5A, which annularly protrudes by apredetermined dimension, and which is integrally die-cast with thesquirrel-cage secondary conductors 5B, and permanent magnets 31 embeddedin the rotor yoke 5A. The permanent magnets 31 are magnetized afterpermanent magnet materials are inserted in slots 44, which will bediscussed hereinafter. The permanent magnets 31 (31SA and 31SB) embeddedin one side (e.g., the right side in the drawing) from the rotatingshaft 6 are polarized with the same south pole, while the permanentmagnets 31 (31NA and 31NB) embedded in the other side (e.g., the leftside in the drawing) are polarized with the same north pole.

[0128] The plurality of squirrel-cage secondary conductors 5B areprovided on the peripheral portion of the rotor yoke 5A and havealuminum diecast members injection-molded in cylindrical holes (notshown) formed in the cage in the direction in which the rotating shaft 6extends. The squirrel-cage secondary conductors 5B are formed in aso-called skew pattern in which they are spirally inclined at apredetermined angle in the circumferential direction of the rotatingshaft 6 from one end toward the other end, as shown in FIG. 5.

[0129] The rotor yoke 5A has a plurality of slots 44 (four in thisembodiment) vertically formed with both ends open. The openings at bothends of the slots 44 are closed by a pair of the end surface members 66and 67, respectively, as shown in FIGS. 6 and 7. When the squirrel-cagesecondary conductors 5B and the end rings 68 and 69 are die-cast, theend surface member 67 is fixed to the rotor yoke 5A by the end ring 69.The end surface member 66 is secured to the rotor yoke 5A by a pluralityof rivets 66A functioning as fixtures.

[0130] In this case, after the permanent magnets 31 are inserted throughthe openings of the slots 44, the openings are closed by the end surfacemember 66, and the end surface member 66 is fixed by riveting intoengaging holes 5C provided in the rotor yoke 5A. This secures thepermanent magnets 31 into the slots 44. The permanent magnets 31 aremade of a rare earth type permanent magnet material of, for example, apraseodymium type permanent magnet or a neodymium type permanent magnetwith nickel plating or the like provided on the surface thereof so as toproduce high magnetic forces. The permanent magnets 31 and 31 areprovided such that they oppose the rotating shaft 6, and the opposingpermanent magnets 31 and 31 are embedded and magnetized to have oppositepoles.

[0131] The permanent magnets 31SA and 31SB embedded in one side (e.g.,the right side and the upper side in the drawing) from the rotatingshaft 6 are polarized with the same south pole, while the permanentmagnets 31NA and 31NB embedded in the other side (e.g., the left sideand the lower side in the drawing) are polarized with the same northpole. More specifically, the permanent magnets 31SA, 31SB and thepermanent magnets 31NA, 31NB are disposed to substantially form arectangular shape around the rotating shaft 6, and are embedded suchthat they carry two poles, namely, the south pole and the north pole,outward in the circumferential direction of the rotating shaft 6. Thisenables torque to be applied to the rotor 5 by the magnetic forces of aprimary winding 7A and an auxiliary winding 7B, which will be discussedhereinafter. The layout of the permanent magnets 31 shown in FIGS. 6 and7 is different from the layout of the permanent magnets 31 shown inFIGS. 2, 3, and 4. The layout of the permanent magnets 31 shown in FIGS.6 and 7 may be replaced by the layout shown in FIGS. 2, 3, and 4. Inthis case, however, the riveting positions of the rivets 66A have to bechanged. Further alternatively, the permanent magnets 31 shown in FIGS.2, 3, and 4 may be arranged as shown in FIG. 6 or 7.

[0132] The hermetic electric compressor C provided with the synchronousinduction motor 2 set forth above is used in a refrigerant circuit (FIG.8) of an air conditioner or an electric refrigerator or the like to coolthe interior of a room or a refrigerator. More specifically, when thecompressor 3 of the hermetic electric compressor C is driven, arefrigerant sealed in the refrigerant circuit is drawn in through asuction pipe 23, compressed by the first rotary cylinder 9 and thesecond rotary cylinder 10, and discharged into a pipe 27 from adischarge pipe 22. The compressed gas refrigerant discharged into thepipe 27 flows into a condenser 28 where it radiates heat and iscondensed into a liquid refrigerant, then flows into a receiver tank 29.

[0133] The liquid refrigerant that flows into and temporarily stays inthe receiver tank 29 passes from a pipe 29A at the outlet side of thereceiver tank 29 to a dryer 30, a moisture indicator 35, a solenoidvalve 36, and a thermostatic expansion valve 37 wherein it is throttled.Then, the liquid refrigerant flows into an evaporator 38 where itevaporates. At this time, the refrigerant absorbs heat around it toeffect its cooling action. When the refrigerant almost liquefies, therefrigerant runs from a pipe 38A at the outlet side of the evaporator 38into an accumulator 39 where it undergoes vapor-liquid separation, thenit is drawn back into the compressor 3 again through a check valve 40.This refrigerating cycle is repeated.

[0134] The liquid refrigerant that has left the receiver tank 29 isbranched off from the pipe 29A into a pipe 38A between the evaporator 38and the accumulator 39 via a capillary tube 41, a high/low pressureswitch 42, and a capillary tube 43. The high/low pressure switch 42detects the pressures of the pipe 29A and the pipe 38A through thecapillary tubes 41 and 43. If the pressures of the two pipes 29A and 38Aexceeds a predetermined pressure difference or more, resulting in aninsufficient amount of the refrigerant drawn into the hermetic electriccompressor C, then the liquid refrigerant from the receiver tank 29 isallowed to flow into the compressor 3 for protection. The thermostaticexpansion valve 37 automatically adjusts its opening degree on the basisof the temperature detected by a thermosensitive cylinder 34 provided atthe outlet end of the evaporator 38.

[0135]FIG. 9 shows an electrical circuit diagram of the synchronousinduction motor 2. The synchronous induction motor 2 shown in FIG. 9that receives power from a single-phase alternating current commercialpower source AC is equipped with a primary winding 7A and an auxiliarywinding 7B. One end of the primary winding 7A is connected to one end ofthe single-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source AC.The auxiliary winding 7B connected to one end of the single-phasealternating current commercial power source AC is connected in series tothe other end of the power source AC through the intermediary of a PTC46 and a start-up capacitor 48 and also connected to an operatingcapacitor 47 in parallel to the PTC 46 and the start-up capacitor 48.

[0136] The PTC 46 is formed of a semiconductor device whose resistancevalue increases in proportion to temperature. The resistance value islow when the synchronous induction motor 2 is started, and increases ascurrent passes therethrough, generating heat. A power switch 49 isconstituted by a current-sensitive type line current sensor fordetecting line current and an overload relay that serves also as aprotective switch used to supply power from the single-phase alternatingcurrent commercial power source AC to the stator winding 7 and to cutoff the supply of power to the stator winding 7. The operating capacitor47 is set to have a capacitance suited for steady operation, and theoperating capacitor 47 and the start-up capacitor 48 are set to providecapacitances suited for start-up in the state wherein the capacitors 47and 48 are connected in parallel.

[0137] The operation of the synchronous induction motor 2 will now bedescribed. When the power switch 49 is closed, current flows from thesingle-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B. When the synchronousinduction motor 2 is started up, the temperature of the PTC 46 is lowand the resistance value thereof is also low, so that large currentpasses through the PTC 46 and large current accordingly passes throughthe auxiliary winding 7B. The auxiliary winding 7B obtains start-uptorque from the current phase difference between itself and the primarywinding 7A produced by the operating capacitor 47 and the start-upcapacitor 48 connected in parallel, thus causing the synchronousinduction motor 2 to start running. This energization causes the PTC 46to start self-heating, and the resistance value of the PTC 46 increasesaccordingly until very little current passes through the PTC 46 itself.Thus, the start-up capacitor 48 is isolated, and the synchronousinduction motor 2 continues steady operation from the current phasedifference between the primary winding 7A and the auxiliary winding 7Bby the operating capacitor 47. As the hermetic electric compressor Coperates, air conditioning is effected in a room or the interior of arefrigerator is cooled.

[0138] As described above, one of the end surface members 67 is securedto the rotor yoke 5A by one of the end rings 69 when the secondaryconductors 5B and the two end rings 68 and 69 are formed. The other endsurface member 66 is secured to the rotor yoke 5A by the rivets 66A.Hence, it is possible to secure the end surface member 67 to the rotoryoke 5A at the same time when the secondary conductors 5B and the endrings 68 and 69 are die-cast. Thus, after the permanent magnets 31 areinserted into the slots 44, the permanent magnets 31 can be secured tothe rotor 5 merely by securing the other end surface member 66 to therotor yoke 5A by the rivets 66A.

[0139] Another rotor 5 is shown in FIG. 10 and FIG. 11. In this case,non-magnetic constituents 55 and 56 are disposed in contact with theinner sides of the two end rings 68 and 69, which are integrallydie-cast with the squirrel-cage type secondary conductors 5B making upthe rotor 5. The non-magnetic constituents 55 and 56 are made of copper,brass, or the like that allows easy passage of current. The thickness ofthe non-magnetic constituents 55 and 56 is set such that, when they areclosely attached onto the plate-like end surface members 66 and 67 thatclose both ends of the permanent magnets 31 embedded in the rotor yoke5A, they do not jut out beyond the end rings 68 and 69 that areintegrally die-cast, protruding from both end surfaces of the rotor yoke5A.

[0140] The non-magnetic constituents 55 and 56 are riveted at both endsthereof by the rivets 66B in the engaging through holes 5C provided inthe rotor yoke 5A. The rivets 66B are fixed at four positions in theinner side of the corners where both ends of the individual permanentmagnets 31SA, 31SB and the permanent magnets 31NA, 31NB are in contact,the permanent magnets being disposed substantially into a rectangularshape around the rotating shaft 6. Thus, the non-magnetic constituents55 and 56 fix the two end surface members 66 and 67 by pressing themagainst the rotor yoke 5A.

[0141]FIG. 12 and FIG. 13 show another rotor 5. As in the case of therotor shown in FIG. 10 and FIG. 11, the non-magnetic constituents 55 and56 are disposed in contact with the inner sides of the two end rings 68and 69, which are integrally die-cast with the squirrel-cage typesecondary conductors 5B making up the rotor 5. The non-magneticconstituents 55 and 56 are made of copper, brass, or the like thatallows easy passage of current. The thickness of the non-magneticconstituents 55 and 56 is set such that, when they are closely attachedonto the plate-like end surface members 66 and 67 that close both endsof the permanent magnets 31 embedded in the rotor yoke 5A, they do notjut out beyond the end rings 68 and 69 that are integrally die-cast,protruding from both end surfaces of the rotor yoke 5A.

[0142] Engaging pins 55A, 55A having a predetermined diameter and apredetermined length are protuberantly formed on one surface of thenon-magnetic constituent 55. Similarly, engaging pins 56A, 56A having apredetermined diameter and a predetermined length are protuberantlyformed on one surface of the non-magnetic constituent 56. Thenon-magnetic constituents 55 and 56 are formed using a cast, and theengaging pins 55A, 55A, 56A, and 56A are integrally formed with thenon-magnetic constituents 55 and 56. The non-magnetic constituents 55and 56 are fixed by being press-fitted into the engaging holes 5Cprovided in the rotor yoke 5A. Thus, the non-magnetic constituents 55and 56 secure the two end surface members 66 and 67 by pressing themagainst the rotor yoke 5A.

[0143] As set forth above, the non-magnetic constituents 55 and 56 aredisposed in contact with the inner sides of the two end rings 68 and 69,and the two end surface members 66 and 67 are secured by being pressedagainst the rotor yoke 5A by the non-magnetic constituents 55 and 56.Therefore, the sectional areas of the end rings 68 and 69 can beincreased by the amount provided by the non-magnetic constituents 55 and56 securing the members 66 and 67 by pressing. With this arrangement,the secondary resistance is decreased by the amount equivalent to theincrease in the sectional areas of the end rings 68 and 69. Hence, arise in temperature of the end rings 69 and 69 can be restrained, andthe magnetic forces of the magnets can be effectively used, making itpossible to significantly improve the running performance of thesynchronous induction motor 2.

[0144] The rotor yoke 5A is provided with a balancer 60 for ensuringgood rotational balance of the rotor 5 (see FIG. 14 and FIG. 15). Thebalancer 60 die-cast into a predetermined shape in advance has an endsurface fixing portion 60A for fixing the end surface member 66 and arested portion 60B placed on the end ring 68, the end surface fixingportion 60A and the rested portion 60B forming a step. The balancer 60is shaped substantially like a semicircle of the rotor yoke 5A. Rivets66C are located substantially equidistantly from the center of thesemicircular balancer 60, and the balancer 60 is secured to the rotoryoke 5A together with the end surface members 66 by the rivets 66C.

[0145] Thus, since the balancer 60 is secured to the rotor yoke 5Atogether with the end surface member 66 by the rivets 66C, the ease ofinstalling the balancer 60 can be dramatically improved. This obviatesthe need for separately fixing the permanent magnets 31 and the balancer60, permitting dramatically improved productivity of the synchronousinduction motor 2.

[0146] A balancer assembly 61 is shown in FIG. 16. The balancer 61 isconstructed of a predetermined number of plate-like balancers 61A andplate-like balancers 61B having substantially the same outerconfiguration as that of the rested portion 60B. The plate-likebalancers 61A are made of metal plates, each plate being made ofstainless steel, copper, brass, or the like and having a predeterminedthickness and having substantially the same outer configuration as thatof the end surface fixing portion 60A of the balancer 60 shown in FIG.14. A predetermined number of the plate-like balancers 61A and apredetermined number of the plate-like balancers 61B are laminated, andsecured to the rotor yoke 5A together with the end surface member 66 bythe rivets 66C, thereby making up the balancer assembly 61.

[0147] Thus, since the balancer assembly 60 is fixed to the rotor yoke5A together with the end surface member 66 by the rivets 66A, greaterease of installation of the balancer 60 can be achieved, allowingconsiderably higher productivity to be achieved. Moreover, since aplurality of the plate-like balancers 61A and 61B are laminated, theweight of the balancer assembly 61 can be easily adjusted. In addition,the cost of the balancer assembly 61 can be significantly reduced byusing, for example, inexpensive metal plates for the balancer assembly61.

[0148]FIG. 17 and FIG. 18 show another balancer assembly 62. Thebalancer assembly 62 is formed of the end surface member 67 and thebalancer 60 shown in FIG. 14 combined into one piece. A weight portion62A corresponding to the balancer 60 and an end surface portion 62Bwhich is formed continuously from the weight 62A and which correspondsto the end surface member 67 are combined into one piece. The balancerassembly 62 is die-cast, or formed by pouring molten copper, brass, orthe like into a mold. The end surface portion 62B and the weight portion62A are secured to the rotor yoke 5A together with the other end surfacemember 67 by a rivet 66B and a rivet 66C, respectively.

[0149] As described above, since the balancer 62 is formed of the endsurface member 67 and the balancer 60 combined into one piece, thenumber of components can be reduced. This allows the installation of theend surface member 67 to be simplified, thus permitting dramaticallyimproved productivity to be achieved.

[0150]FIG. 19 and FIG. 20 show another rotor 5. In this case, the rotoryoke 5A constituting the rotor 5 has a plurality of slots 44 (four inthis embodiment) that are formed to vertically penetrate the rotor yoke5A and have their both ends open. The openings of both ends of the slots44 are closed by a pair of end surface members 66 and 67, as shown inFIG. 19 and FIG. 20. When the squirrel-cage secondary conductors 5B andend rings 68 and 69 are die-cast, the end surface member 67 isintegrally secured to the rotor yoke 5A by the end ring 69, and the endsurface member 66 is integrally secured to the rotor yoke 5A by the endring 68.

[0151] In this case, with the peripheral portions of the end surfacemembers 66 and 67 slightly extended into the end rings 68 and 69,respectively, the rotor yoke 5A, the end rings 68 and 69, and the endsurface members 66 and 67 are die-cast into one piece. This secures thetwo end surface members 66 and 67 to both ends of the rotor yoke 5A, andalso fixes the permanent magnets 31 in the slots 44. The permanentmagnets 31 are made of a rare earth type permanent magnet material of,for example, a praseodymium type permanent magnet or a neodymium typepermanent magnet with nickel plating or the like provided on the surfacethereof so as to produce high magnetic forces. The permanent magnets 31and 31 are provided such that they oppose the rotating shaft 6, and theopposing permanent magnets 31 and 31 are embedded and magnetized to haveopposite poles.

[0152] The permanent magnets 31SA and 31SB embedded in one side (e.g.,the right side and the upper side in the drawing) from the rotatingshaft 6 are polarized with the same south-seeking poles, while thepermanent magnets 31NA and 31NB embedded in the other side (e.g., theleft side and the lower side in the drawing) are polarized with the samenorth-seeking poles. More specifically, the permanent magnets 31SA, 31SBand the permanent magnets 31NA, 31NB are disposed to substantially forma rectangular shape around the rotating shaft 6, and are embedded suchthat they carry two poles, namely, the south pole and the north pole,outward in the circumferential direction of the rotating shaft 6. Thisenables torque to be applied to the rotor 5 by the magnetic forces of aprimary winding 7A and an auxiliary winding 7B, which will be discussedhereinafter. The layout of the permanent magnets 31 shown in FIGS. 19and 20 is different from the layout of the permanent magnets 31 shown inFIGS. 2, 3, and 4. The layout of the permanent magnets 31 shown in FIGS.19 and 20 may be replaced by the layout shown in FIGS. 2, 3, and 4.Further alternatively, the permanent magnets 31 shown in FIGS. 2, 3, and4 may be arranged as shown in FIG. 19 or 20.

[0153] Thus, since the two end surface members 66 and 67 are secured tothe rotor yoke 5A by the two end rings 68 and 69 when the secondaryconductors 5B and the end rings 68 and 69 are formed by die casting, thetwo end surface members 66 and 67 can be easily secured to the rotoryoke 5A when the secondary conductors 5B and the end rings 68 and 69 areformed by die casting. This arrangement makes it possible to obviate theneed of, for example, the cumbersome step for inserting the permanentmagnets 31 into the slots 44, then attaching the end surface members 66and 67 to both ends of the rotor yoke 5A after die-casting the end rings68 and 69, as in the case of a prior art.

[0154] Another rotor is shown in FIGS. 21 and 22. In this case, a rotoryoke 5A is provided with a balancer 60 for ensuring good rotationalbalance of the rotor 5. The balancer 60 is integrally formed with an endsurface member 66, and is constituted by an end surface plate portion60A, a weight portion 60C, and a connecting portion 60B that connectsthe weight portion 60C and the end surface plate portion 60A. The weightportion 60C is formed to have a sufficient size to be rested on an endring 68, and has a substantially semicircular shape.

[0155] The end surface plate portion 60A has substantially the sameshape as the end surface member 66. The end surface plate portion 60Aand the weight portion 60C are connected by the connecting portion 60B.The end surface plate portion 60A, the weight portion 60C, and theconnecting portion 60B are formed into one piece. The balancer 60 iscast by pouring molten copper, brass, or the like into a mold. Theconnecting portion 60B is positioned on the inner side of the end ring68, with the periphery of the end surface plate portion 60A slightlyextending into the end ring 68. The weight portion 60C is formed on theend ring 68.

[0156] The balancer 60 formed as set forth above is secured to the rotoryoke 5A by the end ring 68 when both end surface members 66 and 67,secondary conductors 5B, and the end rings 68 and 69 are die-cast. Theend surface member 67 is secured to the rotor yoke 5A by the end ring69, as previously mentioned. This fixes the permanent magnets 31 inslots 44 of the rotor yoke 5A.

[0157] Thus, the balancer 60 and the end surface member 67 are securedto the rotor yoke 5A when the secondary conductors 5B and the two endrings 68 and 69 are die-cast. This makes it possible to obviate the needfor a cumbersome step for inserting a plurality of the permanent magnets31 into the slots 44 after die-casting the secondary conductor 5B andthe two end rings 68 and 69, then installing the end surface members 66and 67 to both ends of the rotor yoke 5A, as in the prior art.

[0158] When the permanent magnets are installed in the rotor of asynchronous induction motor, a magnetic field of the permanent magnetsinevitably passes through a rotating shaft. Hence, the rotating shaft ismagnetized, and there has been a problem in that iron powder or the likeadheres to the magnetized rotating shaft, causing the rotating shaft towear.

[0159] In addition, installing the permanent magnets in the rotor causesthe rotting shaft and a bearing to be attracted to each other due to themagnetic forces of the permanent magnets, resulting in high frictionbetween the rotating shaft and the bearing. This has also beenpresenting a problem of wear on the rotating shaft.

[0160] Referring now to FIG. 23 through FIG. 37, the descriptions willbe given of the configuration that significantly restrains themagnetization of a rotating shaft to which a rotor of a two-polesynchronous induction motor has been attached.

[0161] In this case, unmagnetized magnet constituents of permanentmagnets 31 are inserted in the openings of slots 44, the openings arethen closed by an end surface member 66, and the end surface member 66is riveted to engaging holes 5C provided in the rotor yoke 5A by rivets66A so as to fix the magnet constituents in the slots 44. Thus, the endsurface members 66 and 67 are secured to both ends of the rotor yoke 5A,and the permanent magnets 31 are fixed in the slots 44. The permanentmagnets 31 are made of a rare earth type permanent magnet material of,for example, a praseodymium type permanent magnet or a neodymium typepermanent magnet with nickel plating or the like provided on the surfacethereof so as to produce high magnetic forces. The permanent magnets 31and 31 are provided such that they oppose the rotating shaft 6, and theopposing permanent magnets 31 and 31 are embedded and magnetized to haveopposite poles, as shown in FIG. 23.

[0162] The permanent magnets 31SA and 31SB embedded in one side (e.g.,the right side and the upper side in the drawing) from the rotatingshaft 6 are polarized with the same south-seeking poles, while thepermanent magnets 31NA and 31NB embedded in the other side (e.g., theleft side and the lower side in the drawing) are polarized with the samenorth-seeking poles. More specifically, the permanent magnets 31SA, 31SBand the permanent magnets 31NA, 31NB are disposed to substantially forma rectangular shape around the rotating shaft 6, and are embedded suchthat they carry two poles, namely, the south pole and the north pole,outward in the circumferential direction of the rotating shaft 6. Thisenables torque to be applied to the rotor 5 by the lines of magneticforce of a primary winding 7A and an auxiliary winding 7B, which will bediscussed hereinafter. The layout of the permanent magnets 31 shown inFIG. 23 is different from the layout of the permanent magnets 31 shownin FIGS. 2, 3, and 4. The layout of the permanent magnets 31 shown inFIG. 23 may be replaced by the layout shown in FIGS. 2, 3, and 4.Further alternatively, the permanent magnets 31 shown in FIGS. 2, 3, and4 may be arranged as shown in FIG. 23.

[0163]FIG. 24 is an analytical diagram of the magnetic field of therotor 5 shown in FIG. 4. In the rotor 5, a magnetic field in which bothpermanent magnets 31 and 31 attract each other is formed; however, onlythe south-pole side of the magnetic field is shown in FIG. 24. As may beseen from FIG. 24 and FIG. 4, The permanent magnets 31 and 31 mounted onthe rotor 5 and opposing the rotating shaft 6 are arranged to haveopposite magnetic poles from each other against the rotating shaft 6.The magnetic flux of the rotor 5 with this arrangement is0.294×10⁻²[Wb], although it depends on the magnetic force of thepermanent magnets 31 and other conditions.

[0164] A lubricant runs between the rotor 5 and the rotating shaft 6,and the rotor yoke 5A in which the permanent magnets 31 have beeninserted is formed of a ferromagnetic member. Therefore, most lines ofmagnetic force (hereinafter referred to as the “magnetic field”) of bothpermanent magnets 31 and 31 pass through the rotor yoke 5A and attracteach other. A part of the magnetic field bypasses the rotor yoke 5A andpasses through the rotating shaft 6 via a void (including a lubricant).It is already well known that a magnetic member easily passes a magneticfield, while the void, which is not a magnetic member, restrains thepassage of the magnetic field; therefore, no further explanation will begiven.

[0165] Measurement results have shown that the magnetic flux density ofthe rotating shaft 6 ranges from about 0.3 teslas up to about 0.42teslas, as shown in FIG. 25, although it depends on the magnetic forcesof the permanent magnets 31 and other conditions. More specifically, themagnetic field of the permanent magnets 31 that passes through therotating shaft 6 magnetizes the rotating shaft 6. The differentpermanent magnets 31 and 31 are laterally disposed in FIG. 4, and thedifferent permanent magnets 31 and 31 are vertically disposed in FIG.24; however, both are the same permanent magnets. In the drawings, thesouth magnetic pole of the permanent magnets 31 is shown, and the northmagnetic pole has been omitted, because a magnetic field symmetrical tothat of the south magnetic pole is produced on the north magnetic poleside.

[0166]FIG. 26 is an analytical diagram of a magnetic field produced whenthe rotor 5 of FIG. 24 is provided with voids 5D. The voids 5D arearcuately formed in the rotor yoke 5A around the rotating shaft 6 andformed such that they are spaced away from the rotating shaft 6 by apredetermined distance and they penetrate in the direction in which therotating shaft 6 extends. The voids 5D are laterally spaced away fromeach other by a predetermined dimension from a point where the permanentmagnet 31 is closest to the rotating shaft 6, and the voids 5D areextended therefrom for a predetermined length and arcuately formedaround the rotating shaft 6. More specifically, since a magnetic fieldis hardly formed in the voids 5D, so that the rotor 5 is provided withthe voids 5D to restrain the passage of a magnetic field so as to alterthe direction of the magnetic field in the rotor 5. The magnetic fluxforce of the rotor 5 in this case is 0.294×10⁻² [Wb].

[0167] In this case, the voids 5D provided in the rotor yoke 5A areformed around the rotating shaft 6, and the magnetic field isaccordingly formed around the rotating shaft 6. However, a part of themagnetic field of the two permanent magnets 31 and 31 passes between thetwo voids 5D and enter the rotating shaft 6. The magnetic flux densityof the rotating shaft 6 ranges from about 0.25 teslas up to about 0.49teslas, as shown in FIG. 27. In other words, since the magnetic field ofthe permanent magnets 31 undesirably passes between the void 5D and thevoid 5D spaced away from each other by the predetermined dimension, therotating shaft 6 located therebetween is magnetized.

[0168]FIG. 28 is an analytical diagram of a magnetic field produced whenthe rotor 5 is provided with a plurality of voids 5D at positionsdifferent from those of the voids 5D shown in FIG. 26. A void 5D isarcuately formed in the rotor yoke 5A around the rotating shaft 6 andformed such that they are spaced away from the rotating shaft 6 by apredetermined distance and it penetrates in the direction in which therotating shaft 6 extends, as mentioned above. The void 5D is laterallyand arcuately formed for a predetermined dimension from a point wherethe permanent magnet 31 is closest to the rotating shaft 6. In addition,arcuate voids 5D are further formed around the rotating shaft 6, withpredetermined dimensions allowed from both ends of the void 5D. In otherwords, the void 5D having a predetermined width is provided at thecentral portion where the permanent magnets 31 and 31 provided in therotor 5 attract each other so as to reduce the magnetic field passingthrough the rotor 5, thereby altering the direction of the magneticfield in the rotor 5. The magnetic flux of the rotor 5 in this case is0.288×10⁻² [Wb].

[0169] In this case also, the voids 5D provided in the rotor yoke 5A areformed around the rotating shaft 6; however, the one of the voids 5Dlaterally extends by a predetermined dimension from the point where thepermanent magnet 31 is closest to the rotating shaft 6, and the magneticfield reduces when it passes through the void 5D. Actually, however, themagnetic field bypasses the voids 5D, as illustrated. In this case, themagnetic field formed by the permanent magnets 31 and 31 bypasses therotating shaft 6 because of the voids 5D. The magnetic flux density ofthe rotating shaft 6 ranges from about 0.23 teslas up to about 0.32teslas, as shown in FIG. 29. In other words, since the magnetic field ofthe permanent magnets 31 avoids passing through the voids 5D, therotating shaft 6 is hardly magnetized.

[0170]FIG. 30 is an analytical diagram showing a magnetic field of therotor 5 when the permanent magnets 31 are disposed at differentpositions. In this case, permanent magnets 31SB are provided between twopermanent magnets 31SA (one of the permanent magnets 31SA is not shown)that oppose the rotating shaft 6 . The permanent magnets 31SB and 31SBare disposed such that they are inclined with respect to the center ofthe permanent magnet 31SA provided on the outer side of the rotor 5. Inother words, the permanent magnets 31SB are inclined in the directionsuch that the flow of the magnetic field of the permanent magnet 31SAmoves away from the rotating shaft 6. This means that the permanentmagnets 31SB and 31SB for drawing in the magnetic field produced by thepermanent magnet 31SA are disposed on both sides of the line that passesthe permanent magnets 31SA and the rotating shaft 6.

[0171] Thus, the flow of the magnetic field of the permanent magnets31SA is directed toward the permanent magnets 31SB. In other words, thepermanent magnets 31SA and the permanent magnets 31SB are disposed toattract each other thereby to change the direction of the magnetic fieldin the rotor 5 so as to cause the magnetic field to pass through therotor yoke 5A excluding the rotating shaft 6. The magnetic flux of therotor 5 in this case is 0.264×10⁻² [Wb]. In this case, the magneticfield produced by the two permanent magnets 31SA is formed such that itbypasses the rotating shaft 6 due to the presence of the permanentmagnets 31SB. The magnetic flux density of the rotating shaft 6 rangesfrom about 0.03 teslas up to about 0.18 teslas, as shown in FIG. 31. Inother words, the magnetic field of the permanent magnets 31 avoidspassing through the rotating shaft 6, so that the rotating shaft 6 ishardly magnetized.

[0172] Based on the analytical results of the magnetic field of therotor 5, the one shown in FIG. 30 wherein the permanent magnets 31SB aredifferently disposed with respect to the permanent magnet 31SA is mosteffective for restraining the magnetization of the rotating shaft 6.This layout of the permanent magnets, however, is not necessarily fullysatisfactory. In comparison, it has been proven that the rotor 5 shownin FIG. 28 in which the voids 5D are provided such that they block themagnetic field between the two permanent magnets 31 and 31, facingagainst the rotating shaft 6, provides the greatest magnetic forcewithout causing the rotating shaft 6 to be magnetized. This means thatthe experiment results have shown that providing the rotor yoke 5A withthe voids 5D shown in FIG. 28 makes it possible to prevent iron powderfrom adhering to the rotating shaft 6 and restrain the degradation inthe performance of the synchronous induction motor 2. Regarding thevoids 5D, only the void 5D provided at the center between the twopermanent magnets 31 and 31 may be provided.

[0173] Examples of the layout of the two-pole permanent magnets 31 aregiven by the rotors 5 shown in FIG. 32 through FIG. 37. Referring toFIG. 32, permanent magnets 31SB, 31SB and permanent magnets 31NB, 31NBare disposed on the right and left sides of the rotating shaft 6 of therotor yoke 5A such that they oppose each other. These permanent magnets31SB, 31SB and the permanent magnets 31NB, 31NB are laid out in “V”shapes such that they face toward the center of the rotating shaft 6. Onthe outer sides of these permanent magnets 31 (on the sides away fromthe rotating shaft 6), a pair of permanent magnets 31 are disposed,opposing each other, to have two poles, the one on the right side of therotating shaft 6 carrying the south pole and the one on the left sidethereof carrying the north pole. Referring to FIG. 33, permanent magnets31SB, 31SB and permanent magnets 31NB, 31NB are further disposed in therotor 5 of FIG. 32 such that they are inclined toward the rotating shaft6. The permanent magnets provide two poles, the ones on the right sideof the rotating shaft 6 carrying the south pole, while the ones on theleft side thereof carrying the north pole.

[0174] Referring now to FIG. 34, two permanent magnets 31 are disposedin the rotor yoke 5A substantially in “V” shapes such that theysubstantially form a diamond shape, laterally opposing each other,sandwiching the rotating shaft 6. The permanent magnet on the right sideof the rotating shaft 6 carries the south pole, while the permanentmagnet on the left side thereof carries the north pole. In other words,in the rotors 5 having the permanent magnets 31 laid out as shown inFIG. 32 through FIG. 34, the magnetization of the rotating shaft 6caused by the magnetic forces of the permanent magnets 31 can berestrained by forming the voids 5D, which is shown in FIG. 28, in therotor yoke 5A as described above, the voids being located at the centralportion where the opposing permanent magnets 31 and 31 attract eachother.

[0175] Referring to FIG. 35, the rotor yoke 5A is provided with eightpermanent magnets 31. The permanent magnets 31 are disposed roughlyradially, as observed from the rotating shaft 6. More specifically, thepermanent magnets 31 are arranged in an approximate radial pattern intwo rows on each side with predetermined intervals provided among thepermanent magnets and with a predetermined space laterally providedbetween the rows on the right side and the left side such that theyoppose each other, sandwiching the rotating shaft 6. The permanentmagnets carry two poles, the ones on the right side of the rotatingshaft 6 carrying the south pole, while the ones on the left side thereofcarrying the north pole. In FIG. 36, the permanent magnets 31 arearranged in an approximate radial pattern in three rows on each sidewith a predetermined interval laterally provided between the rows. Thepermanent magnets carry two poles, the ones on the right side of therotating shaft 6 carrying the south pole, while the ones on the leftside thereof carrying the north pole. In other words, in the rotors 5shown in FIG. 35 and FIG. 36, the permanent magnets 31 are radiallyarranged substantially around the rotating shaft 6, so that the magneticfield is directed away from the rotating shaft 6, as illustrated in FIG.30. Thus, the magnetic field of the two permanent magnets 31 and 31disposed to oppose the rotating shaft 6 bypasses the rotating shaft 6;therefore, the rotating shaft 6 will not be magnetized.

[0176] Referring to FIG. 37, the rotor yoke 5A is provided with sixpermanent magnets 31. These permanent magnets 31 are laid out in asubstantially hexagonal shape around the rotating shaft 6. The permanentmagnets 31 have two poles, the ones on the right side of the rotatingshaft 6 carrying the south pole, while the ones on the left sidecarrying the north pole. By forming the void 5D shown in FIG. 28 in therotor yoke 5A mentioned above at the central portion where the opposingpermanent magnets 31 attract each other, it is possible to furtherrestrain the rotating shaft 6 from being magnetized by the magneticforces of the permanent magnets 31. More specifically, in the rotor 5provided with the permanent magnets 31 disposed as shown in FIG. 37, thevoids 5D provided in the rotor 5 shown in FIG. 26 cause the magneticfields of the two opposing permanent magnets 31 to pass the rotor yoke5A, bypassing the voids 5D. As a result, the magnetic fields do not passthe rotating shaft 6, so that the rotating shaft 6 is hardly magnetized.Voids 32 shown in FIGS. 33, 34, and 37 intercept the magnetic fieldformed between the permanent magnets 31 on the south pole side and thepermanent magnets 31 on the north pole side. The voids 32, however, aredispensable.

[0177] As described above, the voids 5D are formed at the centralportion of the rotor yoke 5A where the permanent magnets 31 and 31,which oppose each other with the rotating shaft 6 sandwichedtherebetween and attract each other, and the permanent magnets 31 arearranged such that the magnetic field does not pass through the rotatingshaft 6 or the magnetic field bypasses the rotating shaft 6. With thisarrangement, it is possible to restrain the rotating shaft 6 from beingmagnetized. This makes it possible to prevent inconveniences in whichiron powder or the like adheres to the rotating shaft 6 or the rotatingshaft 6 and the bearings 17 and 18 wear out due to friction caused bythe magnetic forces of the permanent magnets 31.

[0178] In general, the permanent magnets used with synchronous inductionmotors are magnetized in advance at a different place, then installed inrotors. For this reason, when inserting the magnetized permanent magnetsin rotors, the permanent magnets attract each other, leading to poorworkability. Furthermore, when inserting a rotor in a stator, the rotoris attracted to a surrounding surface, posing the problem of degradedassemblability of a synchronous induction motor.

[0179] In addition, since the permanent magnets are incorporated in arotor, the workability in installing the rotor in a stator is degraded,resulting in assembly failure.

[0180] Referring now to FIG. 38 through FIG. 46, the descriptions willbe given to the structure of a synchronous induction motor that allowspermanent magnets to be inserted in a rotor without the magneticattraction problem of the permanent magnets, and that also featuresdramatically improved workability of installation. The descriptions willalso be given of a manufacturing method for the synchronous inductionmotor.

[0181] The rotor 5 in this case is constructed of a rotor yoke 5A,die-cast squirrel-cage secondary conductors 5B positioned around therotor yoke 5A, a die-cast end ring 69 which is positioned on theperipheral portion of an end surface of the rotor yoke 5A, annularlyprotrudes by a predetermined dimension, and integrally die-cast with thesquirrel-cage secondary conductors 5B, and permanent magnets 31 embeddedin the rotor yoke 5A. The permanent magnets 31 are magnetized afterpermanent magnet materials are inserted in slots 44, which will bediscussed hereinafter. The permanent magnets 31 (31SA and 31SB) embeddedin one side (e.g., the right side in the drawing) from the rotatingshaft 6 are polarized with the same south pole, while the permanentmagnets 31 (31NA and 31NB) embedded in the other side (e.g., the leftside in the drawing) are polarized with the same north pole, as shown inFIG. 38 and FIG. 39.

[0182] The plurality of squirrel-cage secondary conductors 5B areprovided on the peripheral portion of the rotor yoke 5A and havealuminum diecast members injection-molded in cylindrical holes (notshown) formed in the cage in the direction in which the rotating shaft 6extends, as described previously. The squirrel-cage secondary conductors5B are formed in a so-called skew pattern in which they are spirallyinclined at a predetermined angle in the circumferential direction ofthe rotating shaft 6 from one end toward the other end, as illustratedin FIG. 5.

[0183] The rotor yoke 5A has a plurality of slots 44 (four in thisembodiment) vertically formed with both ends open. The openings at bothends of the slots 44 are closed by a pair of the end surface members 66and 67, respectively, as shown in FIG. 7. When the squirrel-cagesecondary conductors 5B and the end rings 68 and 69 are die-cast, theend surface member 67 is fixed to the rotor yoke 5A by the end ring 69.The end surface member 66 is secured to the rotor yoke 5A by a pluralityof rivets 66A functioning as fixtures.

[0184] In this case, after the unmagnetized magnet constituents of thepermanent magnets 31 are inserted through the openings of the slots 44,the openings are closed by the end surface member 66, and the endsurface member 66 is fixed by riveting into engaging holes 5C providedin the rotor yoke 5A by using the rivets 66A. This secures the magnetconstituents in the slots 44. The magnet constituents are formed of arare earth type permanent magnet material of, for example, apraseodymium type permanent magnet or a neodymium type permanent magnetwith nickel plating or the like provided on the surface thereof, or aferrite material, that is capable of exhibiting high magnetcharacteristics even in a low magnetizing magnetic field. In this case,the demagnetization during operation can be restrained by using, forexample, a ferrite magnet or a rare earth type magnet (the coerciveforce at normal temperature being 1350 to 2150 kA/m and the coerciveforce temperature coefficient being 0.7%/° C. or less).

[0185] If an unmagnetized magnet constituent is inserted in a rotor, anda stator winding is energized to magnetize the magnet constituent, thestator winding may be deformed by the electromagnetic force produced atthe magnetization. For this reason, the stator winding 7 is coated withvarnish or a sticking agent that fuses when heated. The varnish or thesticking agent that fuses when heated securely prevents the deformationof a winding end of the stator winding 7 and the degradation of thecoating of the winding caused by heat if the stator winding 7 becomeshot from the heat generated by itself when the magnet constituent ismagnetized.

[0186] There is another problem in that the quality of a synchronousinduction motor is deteriorated. To solve the problem, a predeterminedvoltage and a predetermined current are supplied to one phase or twophases of the stator winding so as to magnetize the unmagnetized magnetconstituents fixed in the slots 44 provided in the rotor yoke 5A. Thispermits better magnetizing performance than that obtained by energizingthe primary winding 7A and the auxiliary winding 7B at the same time.Hence, the unmagnetized magnet constituents can be intensely magnetized.

[0187] The rotor 5 is provided with four permanent magnets 31 and 31formed of the magnetized magnet constituents that oppose the rotatingshaft 6. The opposing permanent magnets 31 and 31 are disposed withopposite magnetic poles, as shown in FIG. 40. Permanent magnets 31SA and31SB embedded in one side of the rotating shaft 6 (e.g., upper and loweron the right side in the drawing) from the rotating shaft 6 arepolarized with the same south pole, while the permanent magnets 31NA and31NB embedded in the other side (e.g., upper and lower on the left sidein the drawing) are polarized with the same north pole.

[0188] More specifically, the permanent magnets 31SA, 31SB and thepermanent magnets 31NA, 31NB are disposed to substantially form arectangular shape around the rotating shaft 6, and are embedded suchthat they carry two poles, namely, the south pole and the north pole,outward in the circumferential direction of the rotating shaft 6. Thisenables torque to be applied to the rotor 5 by the magnetic forces of aprimary winding 7A and an auxiliary winding 7B, which will be discussedhereinafter. The layout of the permanent magnets 31 shown in FIG. 40 isdifferent from the layout of the permanent magnets 31 shown in FIG. 38;however, the layout of the permanent magnets 31 shown in FIG. 40 may bereplaced by the layout shown in FIG. 38. In this case, however, theriveting positions of the rivets 66A have to be changed. Furtheralternatively, the permanent magnets 31 shown in FIG. 38 may be arrangedas shown in FIG. 40.

[0189] Thus, after the magnet constituents of the permanent magnets 31are embedded in the rotor yoke 5A, the magnet constituents aremagnetized by current passed through the stator winding 7. Hence, whenthe rotor 5 is inserted in the stator 4, a problem can be solved inwhich the permanent magnets 31 inserted in the stator 4 cause magneticattraction to the surrounding. This arrangement makes it possible toprevent inconvenience of lower productivity of the synchronous inductionmotor 2, thus permitting improved assemblability of the synchronousinduction motor 2.

[0190] Another rotor 5 is shown in FIG. 41. In this case, the rotor yoke5A has two magnet constituents embedded therein. The two plate-likemagnet constituents are arranged in parallel to each other, sandwichingthe rotating shaft 6 and embedded in slots 44 vertically formed in therotor yoke 5A so that they penetrate the rotor yoke 5A. The magnetconstituents are formed of a rare earth type or ferrite material, asmentioned above.

[0191] Referring now to FIG. 46, a three-phase, two-pole synchronousinduction motor 2A will be described. The synchronous induction motor 2Ais installed in the hermetic electric compressor C, as in the case ofthe synchronous induction motor 2 described above. FIG. 46 is anelectrical circuit diagram of the three-phase, two-pole synchronousinduction motor 2A. In the drawing, the synchronous induction motor 2Ais equipped with a three-phase stator winding 75 constructed of awinding 75A, a winding 75B, and a winding 75C. The winding 75A, thewinding 75B, and the winding 75C of the stator winding 75 are connectedto a three-phase alternating current commercial power source AC3 throughthe intermediary of a power switch 77. Current-sensitive line currentdetectors 76 for detecting line current are provided on the linesconnected to the winding 75A, the winding 75B, and the winding 75C. Thepower switch 77 functions also as a protective switch that cuts off thesupply of power to the stator winding 7 if any of the line currentdetectors 76 senses a predetermined current. The rest of theconfiguration is as described above.

[0192] The two unmagnetized magnet constituents fixed in the slots 44provided in the rotor yoke 5A are magnetized by a predetermined voltageand a predetermined current supplied to one phase, two phases, or threephases of the stator winding. Thus, the two opposing magnet constituentsare magnetized into the permanent magnets 31 having opposite magneticpolarities. To be more specific, the rotor 5 includes opposing permanentmagnets 31 magnetized to have opposite magnetic polarities, namely,permanent magnets 31SA on the right side and permanent magnets 31NA onthe left side.

[0193] Another example of the rotor 5 is shown in FIG. 42. In this casealso, the rotor yoke 5A is provided with two magnet constituents. Thetwo magnet constituents are embedded in slots 44 vertically formed inthe rotor yoke 5A so that they penetrate the rotor yoke 5A. The magnetconstituents are disposed in arcuate shapes inside the squirrel-cagesecondary conductor 5B with a predetermined interval allowedtherebetween, and are embedded such that both ends of the two arcuatemagnet constituents are close to each other. The magnet constituents isformed of a rare earth type or ferrite material, as mentioned above.

[0194] The two unmagnetized magnet constituents fixed in the slots 44provided in the rotor yoke 5A are magnetized by a predetermined voltageand a predetermined current supplied to one phase, two phases, or threephases of the stator winding. Thus, the two opposing magnet constituentsare magnetized into the permanent magnets 31 having opposite magneticpolarities to constitute the rotor 5. To be more specific, the rotor 5includes opposing permanent magnets 31 magnetized to have oppositemagnetic polarities, namely, a permanent magnet 31SA on the right sideand a permanent magnet 31NA on the left side.

[0195] Another example of the rotor 5 is shown in FIG. 43. In this case,the rotor yoke 5A is provided with four magnet constituents. The fourmagnet constituents are individually embedded in slots 44 verticallyformed in the rotor yoke 5A such that they penetrate the rotor yoke 5A.The magnet constituents are embedded inside the squirrel-cage secondaryconductor 5B such that two sets of permanent magnets 31, each setconsisting of two magnet constituents and shaping substantially like“V”, oppose each other, sandwiching the rotating shaft 6. The magnetconstituents are arranged such that they form substantially a diamondshape, as observed from above. The magnet constituents are formed of arare earth type or ferrite material, as previously mentioned. Voids 32function to intercept the magnetic field formed between the south pole(permanent magnets 31SA, 31SB) and the north pole (permanent magnets31NA, 31NB). The voids 32, however, are dispensable.

[0196] The unmagnetized magnet constituents fixed in the slots 44provided in the rotor yoke 5A are magnetized by a predetermined voltageand a predetermined current supplied to one phase, two phases, or threephases of the stator winding. Thus, the opposing sets of magnetconstituents are magnetized into the sets of permanent magnets 31carrying opposite magnetic polarities. To be more specific, the rotor 5includes opposing sets of permanent magnets 31 magnetized to haveopposite magnetic polarities, namely, two upper and lower permanentmagnet 31SA and 31SB on the right side and two upper and lower permanentmagnet 31NA and 31NB on the left side.

[0197] Another example of the rotor 5 is shown in FIG. 44. In this case,the rotor yoke 5A is provided with six magnet constituents. The sixmagnet constituents are individually embedded in slots 44 verticallyformed in the rotor yoke 5A such that they penetrate the rotor yoke 5A.The magnet constituents are arranged inside the squirrel-cage secondaryconductor 5B such that two sets, each set consisting of three magnetconstituents, oppose each other, sandwiching the rotating shaft 6therebetween, and are shaped like a hexagon. The magnet constituents areformed of a rare earth type or ferrite material, as previouslymentioned.

[0198] The unmagnetized magnet constituents fixed in the slots 44provided in the rotor yoke 5A are magnetized by a predetermined voltageand a predetermined current supplied to one phase, two phases, or threephases of the stator winding. Thus, the opposing sets of magnetconstituents are magnetized into the sets of permanent magnets 31carrying opposite magnetic polarities. To be more specific, the rotor 5includes opposing sets of permanent magnets 31 magnetized to haveopposite magnetic polarities, namely, three permanent magnets 31SA,31SB, and 31SC on the right side and three permanent magnets 31NA, 31NB,and 31NC on the left side.

[0199] Another example of the rotor 5 is shown in FIG. 45. In this case,the rotor yoke 5A is provided with eight magnet constituents. The eightmagnet constituents are individually embedded in slots 44 verticallyformed in the rotor yoke 5A such that they penetrate the rotor yoke 5A.The magnet constituents are arranged inside the squirrel-cage secondaryconductor 5B such that two sets, each set consisting of four magnetconstituents, oppose each other, sandwiching the rotating shaft 6therebetween, and are shaped like an octagon. The magnet constituentsare formed of a rare earth type or ferrite material, as previouslymentioned.

[0200] The unmagnetized magnet constituents fixed in the slots 44provided in the rotor yoke 5A are magnetized by a predetermined voltageand a predetermined current supplied to one phase, two phases, or threephases of the stator winding. Thus, the opposing sets of magnetconstituents are magnetized into the sets of permanent magnets 31carrying opposite magnetic polarities. To be more specific, the rotor 5includes opposing sets of permanent magnets 31 magnetized to haveopposite magnetic polarities, namely, four permanent magnets 31SA, 31SB,31SC, and 31SD on the right side and four permanent magnets 31NA, 31NB,31NC, and 31ND on the left side.

[0201] Thus, it is possible to magnetize a plurality of unmagnetizedmagnet constituents inserted in the rotor 5 either at once or in aplurality of number of times. This arrangement makes it possible toenergize either one phase or two phases of windings to effect themagnetization if a winding or the like deforms due to heat generatedduring magnetization. Even if windings are not deformed by heatgenerated during magnetization, either one phase or two phases ofwindings may be selected and energized to magnetize at once. This makesit possible to efficiently magnetize a plurality of unmagnetized magnetconstituents inserted in the rotor 5, leading to dramatically improvedproductivity of the synchronous induction motor 2.

[0202] An air conditioner or an electric refrigerator or the likerequires large motion torque at the time of start-up, so that itincorporates a motor that provides larger motion torque than steadymotion torque required for normal operation. Increasing the motiontorque for starting a synchronous induction motor inevitably increasespower consumed during normal operation. Therefore, the motion torque forstarting the motor used in a hermetic electric compressor constituting arefrigerating cycle of a refrigerator or an air conditioner has not beenentirely adequate in achieving higher efficiency to meet recent energyregulations. For this reason, there has been demand for developing adrive unit for a synchronous induction motor that consumes less powerduring normal operation and secures sufficient motion torque at astart-up at the same time.

[0203] Referring to FIG. 47 through FIG. 52, the descriptions will nowbe given of a drive unit for a synchronous induction motor that consumesless power during normal operation and provides high motion torque at astart-up.

[0204]FIG. 47 is an electrical circuit diagram of a drive unit T1 of asynchronous induction motor 2 that exhibits the aforesaid features.Referring to FIG. 47, the synchronous induction motor 2 that receivespower from a single-phase alternating current commercial power source ACis equipped with a stator winding 7 constructed of a primary winding 7Aand an auxiliary winding 7B. One end of the primary winding 7A isconnected to one end of the single-phase alternating current commercialpower source AC, and the other end thereof is connected to the other endof the single-phase alternating current commercial power source ACthrough the intermediary of a socket terminal 51. One end of theauxiliary winding 7B is connected to one end of the single-phasealternating current commercial power source AC, and the other endthereof is connected to the other end of the single-phase alternatingcurrent commercial power source AC through the intermediary of a socketterminal 51 and an operating capacitor 47. A power switch 49 isconstituted by a current-sensitive type line current sensor fordetecting line current and an overload relay that serves also as aprotective switch used to supply power from the single-phase alternatingcurrent commercial power source AC to the stator winding 7 and to cutoff the supply of power to the stator winding 7. The operating capacitor47 is set to have a capacitance suited for start-up and steady operationof the synchronous induction motor 2.

[0205] When the power switch 49 is turned ON to supply power from thesingle-phase alternating current commercial power source AC, theparallel circuit of the operating capacitor 47 and the primary winding7A is connected to the auxiliary winding 7B. By the current phasedifference between the primary winding 7A and the auxiliary winding 7B,the synchronous induction motor 2 obtains a start-up motion torque tostart running. The synchronous induction motor 2 continues its steadyoperation from the current phase difference between the primary winding7A and the auxiliary winding 7B produced by the operating capacitor 47.In this case, the operating capacitor 47 serves also as a start-upcapacitor.

[0206]FIG. 48 is an electrical circuit diagram of another drive unit T2for a synchronous induction motor 2. Referring to FIG. 48, thesynchronous induction motor 2 receiving power from a single-phasealternating current commercial power source AC is also equipped with astator winding 7 constructed of a primary winding 7A and an auxiliarywinding 7B. The stator winding 7 is connected to the single-phasealternating current commercial power source AC through the intermediaryof a power switch 49. The primary winding 7A connected to one end of thesingle-phase alternating current commercial power source AC is connectedto the other end of the single-phase alternating current commercialpower source AC through the intermediary of a socket terminal 51. Theauxiliary winding 7B connected to one end of the single-phasealternating current commercial power source AC is connected to the powerswitch 49 through the intermediary of the socket terminal 51 and a relaycoil 45A of a start-up relay 45.

[0207] The auxiliary winding 7B is connected in series to the other endof the single-phase alternating current commercial power source ACthrough the intermediary of a socket terminal 51, a start-up relaycontact 45B of the start-up relay 45, and a start-up capacitor 48. Theoperating capacitor 47 is connected in parallel to the start-up relaycontact 45B and the start-up capacitor 48. The operating capacitor 47 isset to provide a capacitance suited for steady operation. In a statewherein the operating capacitor 47 and the start-up capacitor 48 areconnected in parallel, the capacitors 47 and 48 are set to capacitancessuited for a start-up. Very little current passes the relay coil 45A atan operation start when large current passes through the synchronousinduction motor 2. When the synchronous induction motor 2 moves to itssteady operation with the start-up relay contact 45B closed, currentpasses through the relay coil 45A, and the start-up relay contact 45B isopened, isolating the start-up capacitor 48.

[0208] The moment the power switch 49 is turned ON, current flows fromthe single-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B. When large currentpasses through the auxiliary winding 7B at the start-up of thesynchronous induction motor 2, very little current passes through therelay coil 45A; therefore, the start-up relay contact 45B of thestart-up relay 45 remains closed, and the auxiliary winding 7B providesstart-up motion torque from the current phase difference from theprimary winding 7A provided by the operating capacitor 47 and thestart-up capacitor 48 connected in parallel thereto, thus causing thesynchronous induction motor 2 to start running. As the synchronousinduction motor 2 shifts to its steady operation, the current passingthrough the auxiliary winding 7B decreases, causing current to passthrough the relay coil 45A. The magnetomotive force of the relay coil45A turns the power switch 49 OFF to isolate the start-up capacitor 48.The synchronous induction motor 2 continues its steady operation by thecurrent phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47.Alternatively, the use of the start-up relay 45 may be replaced bycurrent control based on a thyristor.

[0209]FIG. 49 is an electrical circuit diagram of another drive unit T3for the synchronous induction motor 2. Referring to FIG. 49, thesynchronous induction motor 2 receiving power from a single-phasealternating current commercial power source AC is also equipped with astator winding 7 constructed of a primary winding 7A and an auxiliarywinding 7B. The stator winding 7 is connected to the single-phasealternating current commercial power source AC through the intermediaryof a power switch 49. One end of the primary winding 7A is connected toone end of the single-phase alternating current commercial power sourceAC, and the other end thereof is connected to the other end of thesingle-phase alternating current commercial power source AC. One end ofthe auxiliary winding 7B is connected to one end of the single-phasealternating current commercial power source AC, and the other endthereof is connected to the other end of the single-phase alternatingcurrent commercial power source AC through the intermediary of apositive thermistor 46 (hereinafter referred to as “PTC). An operatingcapacitor 47 is connected in parallel to the PTC 46. The PTC 46 is asemiconductor device whose resistance value increases with increasingtemperature. The resistance value of the PTC 46 is low when thesynchronous induction motor 2 is started, but it increases as the PTC 46generates heat due to the passage of current.

[0210] The moment the power switch 49 is turned ON, current flows fromthe single-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B, causing the synchronousinduction motor 2 to start up. When the synchronous induction motor 2 isstarted up, the temperature of the PTC 46 is low and its resistancevalue is low; therefore, large current passes through the PTC 46, andlarge current accordingly passes through the auxiliary winding 7B (thecurrent passing through the operating capacitor 47 being small). Thisenergization causes the PTC 46 to start self-heating, and the resistancevalue of the PTC 46 increases accordingly until very little currentpasses through the PTC 46 itself. Thus, the synchronous induction motor2 continues steady operation from the current phase difference betweenthe primary winding 7A and the auxiliary winding 7B by the operatingcapacitor 47.

[0211]FIG. 50 is an electrical circuit diagram of another drive unit T4for the synchronous induction motor 2. The construction of the driveunit T4 is the same as that shown in FIG. 9. The construction will beexplained again in detail. The synchronous induction motor 2 receivingpower from a single-phase alternating current commercial power source ACis also equipped with a stator winding 7 constructed of a primarywinding 7A and an auxiliary winding 7B. The stator winding 7 isconnected to the single-phase alternating current commercial powersource AC through the intermediary of a power switch 49. One end of theprimary winding 7A is connected to one end of the single-phasealternating current commercial power source AC, and the other endthereof is connected to the other end of the single-phase alternatingcurrent commercial power source AC. One end of the auxiliary winding 7Bis connected to one end of the single-phase alternating currentcommercial power source AC, and the other end thereof is connected inseries to the other end of the single-phase alternating currentcommercial power source AC through the intermediary of a PTC 46 and astart-up capacitor 48. An operating capacitor 47 is connected inparallel to the PTC 46 and the start-up capacitor 48.

[0212] When the power switch 49 is closed, current flows from thesingle-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B. When the synchronousinduction motor 2 is started up, the temperature of the PTC 46 is lowand the resistance value thereof is also low, so that large currentpasses through the PTC 46 and large current accordingly passes throughthe auxiliary winding 7B. The auxiliary winding 7B obtains start-uptorque from the current phase difference between itself and the primarywinding 7A produced by the operating capacitor 47 and the start-upcapacitor 48 connected in parallel, thus causing the synchronousinduction motor 2 to start running. This energization causes the PTC 46to start self-heating, and the resistance value of the PTC 46 increasesaccordingly until very little current passes through the PTC 46 itself.Thus, the start-up capacitor 48 is isolated, and the synchronousinduction motor 2 continues steady operation from the current phasedifference between the primary winding 7A and the auxiliary winding 7Bby the operating capacitor 47.

[0213]FIG. 51 shows the relationship between rotating torque T providedby the electric circuit of each of the drive units T1, T2, T3, and T4set forth above, and a number of revolutions n. In the chart, the axisof ordinates indicates a rotating torque T, the rotating torque T is thesmallest at the bottom, and is higher at a higher level. The axis ofabscissa indicates the number of revolutions n, the left end thereofbeing the smallest number of revolutions n, while the right end beingthe largest number of revolutions n. The two-dot chain curve denotes therotating torque T in relation to the number of revolutions n of thedrive unit T1, and the solid-line curve denotes the rotating torque T inrelation to the number of revolutions n of the drive unit T3. The dashedline curve denotes the rotating torque T in relation to the number ofrevolutions n of the drive unit T4, and the one-dot chain curve denotesthe rotating torque T in relation to the number of revolutions n of thedrive unit T2.

[0214] As can be seen from the chart, the drive unit T1 having a singlecapacitor that serves as the starting capacitor 48 and the operatingcapacitor 47 exhibits low start-up operating torque and low steadyoperating torque. The drive unit T1, however, obviates the need for thestart-up relay 45 and other elements, so that it is used with an airconditioner or other equipment, such as an electric refrigerator, thathas relatively low start-up operating torque and steady operatingtorque.

[0215] The drive unit T2 that switches between the start-up capacitor 48and the operating capacitor 47 by the start-up relay 45 provides higherstart-up operating torque. As the number of revolutions n of thesynchronous induction motor 2 increases, leading to the shift to thesteady operation mode, current passes through the relay coil 45A,causing the start-up relay contact 45B to open thereby to isolate thestart-up capacitor 48. Thereafter, the drive unit T2 performs the sameoperation as that of the drive unit T3 at the rotating torque T inrelation to the number of revolutions n. Thus, the operating torque forstarting up the synchronous induction motor 2 can be increased, whilethe power consumed during the steady operation can be reduced,permitting the synchronous induction motor 2 to be operated at extremelyhigh efficiency. The drive unit T2 provides higher operating torque forstart-up and higher operating torque for steady operation, so it is usedwith an air conditioner or other equipment, such as an electricrefrigerator, that has relatively high start-up operating torque andsteady operating torque.

[0216] The drive unit T3 that uses the PTC 46, which is a semiconductordevice whose resistance value increases with increasing temperature, andthe operating capacitor 47 provides a higher start-up rotating torquethan the drive unit T1. The drive unit T3 obviates the need for thestart-up relay 45 and other devices, and secures higher reliability.This makes it possible to allow a higher operating torque to be obtainedat the start-up of the synchronous induction motor 2, and to reduce thepower consumed during normal operation, thus enabling the synchronousinduction motor 2 to be operated with extremely high efficiency. Thedrive unit T3, therefore, is used with an air conditioner or otherequipment, such as an electric refrigerator, that has relatively lowstart-up operating torque and steady operating torque and is required toexhibit high reliability.

[0217] The drive unit T4 that uses the PTC 46, which is a semiconductordevice whose resistance value increases with increasing temperature, thestart-up capacitor 48, and the operating capacitor 47 provides a stillhigher start-up rotating torque T than the drive unit T3, permittingeven higher reliability to be achieved. This makes it possible to allowa higher operating torque to be obtained at the start-up of thesynchronous induction motor 2, and to reduce the power consumed duringnormal operation, thus enabling the synchronous induction motor 2 to beoperated with extremely high efficiency. The drive unit T4, therefore,is used with an air conditioner or other equipment, such as an electricrefrigerator, that has relatively high start-up operating torque andsteady operating torque and is required to exhibit high reliability.

[0218]FIG. 52 is a refrigerant circuit of an air conditioner or otherequipment, such as an electric refrigerator, that uses a hermeticelectric compressor C incorporating a synchronous induction motor 2. Therefrigerant circuit has added a liquid injection circuit 58 to therefrigerant circuit shown in FIG. 8. A receiver tank 29 provided in therefrigerant circuit is connected to a compressor 3 of the hermeticelectric compressor C through the intermediary of a strainer 52, asolenoid valve 53, and a capillary tube 54.

[0219] The solenoid valve 53 is connected to a thermosensor 57 connectedto a pipe 27 located at the discharge end of the compressor 3, and theopening degree thereof is automatically adjusted according to thetemperature detected by the thermosensor 57. When the compressor 3 ofthe hermetic electric compressor C is driven, the refrigerant sealed inthe refrigerant circuit is drawn in through a suction pipe 23 andcompressed in steps by a first rotary cylinder 9 and a second rotarycylinder 10, then discharged into the pipe 27 through a discharge pipe22. The compressed gas refrigerant discharged into the pipe 27 flowsinto a condenser 28 wherein it radiates heat and condenses into a liquidrefrigerant which flows into the receiver tank 29. A part of the liquidrefrigerant leaving the receiver tank 29 flows also into the liquidinjection circuit 58 and further passes through the strainer 52 and thesolenoid valve 53 to reach the capillary tube 54 wherein it is throttledbefore being discharged into a compressor 3. The liquid refrigerantdischarged into the compressor 3 evaporates therein when it absorbs heatso as to cool the compressor 3. This restrains a temperature rise in thecompressor 3 in a cooling operation mode thereby to protect thecompressor 3. The rest of the operation is the same as previouslydescribed.

[0220] Hitherto, the stator winding constituting the synchronousinduction motor of this type of hermetic electric compressor isthermally protected primarily by actuating a thermostat wrapped aroundthe stator winding to cut off the supply of power to the synchronousinduction motor. Alternatively, a temperature sensor is attached to thedischarge pipe or the suction pipe of the hermetic electric compressoror to the outer surface of the hermetic vessel, and if the temperatureof the hermetic electric compressor reaches a preset value or more, aprotective switch is actuated by the temperature sensor to cut off thesupply of power to the synchronous induction motor so as to protect thehermetic electric compressor.

[0221] In a conventional hermetic electric compressor, if thetemperature of the stator winding rises due to an overloaded operation,in order to protect the stator winding of the synchronous inductionmotor from being burnt, the thermostat wrapped around the stator windingis actuated to cut off the supply of power to the synchronous inductionmotor. Alternatively, an expensive circuit device using a thermistor orthe like is installed on the discharge pipe, and if a dischargetemperature reaches a reference level or more, then the supply of powerto the synchronous induction motor is cut off thereby to protect thesynchronous induction motor from abnormal temperatures. In this case,the difference between the actual temperature of the stator winding andthe discharge temperature greatly varies according to load conditions,etc. Hence, there has been a problem in that the operation of thesynchronous induction motor is actually continued while the temperatureof the stator winding is higher than the reference level, leading to amarkedly shortened service life of the synchronous induction motor.There has been another problem in that the stator winding is burnt.

[0222] There has been still another problem in that a rise in thetemperature of the synchronous induction motor causes the permanentmagnets embedded in the rotor yoke to be thermally demagnetized,resulting in reduced driving power of the synchronous induction motor.

[0223] Referring now to FIG. 53 through FIG. 66, a hermetic electriccompressor capable of restraining a rise in temperature of the statorwinding and of securely preventing permanent magnets from beingthermally demagnetized will be described.

[0224] In this case, a hermetic vessel 1 of a hermetic electriccompressor C is divided into two parts, namely, a cylindrical shell 1Ahaving an open upper end and an end cap 1B that closes the open upperend. An electric unit and a compression unit (hereinafter referred to as“the synchronous induction motor 2” and “the compressor 3”) are housedin the shell 1A, the end cap 1B is attached to the shell 1A so as tocover the shell 1A, then they are sealed by high-frequency welding orthe like.

[0225] The hermetic electric compressor C is provided with a thermistor46 serving as a thermal protective device whose resistance value changeswith temperature. The thermistor 46 is attached to a stator winding 7provided in the hermetic vessel 1 of the hermetic electric compressor C.The thermistor 46 is secured to the stator winding 7 by a polyester yarn70 binding the coil end of the stator winding 7. Furthermore, thethermistor 46 is connected to a connection terminal 71 provided on theend cap 1B of the hermetic vessel 1 by a lead wire 72, as shown in FIG.53.

[0226]FIG. 54 is an electrical circuit diagram of the synchronousinduction motor 2 in this embodiment. Referring to FIG. 54, thesynchronous induction motor 2, which receives power from a single-phasealternating current commercial power source AC, is equipped with astator winding 7 formed of a primary winding 7A and an auxiliary winding7B. One end of the primary winding 7A is connected to one end of thesingle-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source AC.One end of the auxiliary winding 7B is connected to one end of thesingle-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source ACthrough the intermediary of an operating capacitor 47.

[0227] One end of the auxiliary winding 7B is connected to the other endof the single-phase alternating current commercial power source ACthrough the intermediary of a contact 61B of a start-up relay 61 andstart-up capacitors 48 and 48. These contact 61B and the start-upcapacitors 48 and 48 are connected in series, and the operatingcapacitor 47 is connected in parallel to the contact 61B and thestart-up capacitors 48 and 48. The operating capacitor 47 is set to acapacitance suited for steady operation. In the state wherein theoperating capacitor 47 and the start-up capacitors 48 and 48 areconnected in parallel, the capacitors 47, 48, and 48 are set tocapacitances suited for start-up. Reference numerals 48A and 48A denotedischarge resistors for discharging currents charged in the start-upcapacitors 48 and 48, reference numeral 61A denotes a start-up relaycoil, and reference character PSW denotes a power switch.

[0228] A control relay 49 is provided that is connected between thepower switch PSW and the stator winding 7 and provided with a controlrelay contact 49B to supply power from the single-phase alternatingcurrent commercial power source AC to the stator winding 7 and to cutoff the supply of power to the stator winding 7. A controller 62controls the supply of power to the synchronous induction motor 2according to a change in the resistance value of the thermistor 46. Thecontroller 62 is connected to the thermistor 46 secured to the statorwinding 7 and also connected to a control relay coil 49A of the controlrelay 49. Connected to the controller 62 is a current-sensitive linecurrent detector 63 that is connected to one end of the single-phasealternating current commercial power source AC and that functions as anoverload protective device for detecting line current.

[0229] When the power switch PSW is turned ON with the control relaycontact 49B closed, current is supplied from the single-phasealternating current commercial power source AC to the primary winding 7Aand the auxiliary winding 7B. At the start-up of the synchronousinduction motor 2, current passes through a start relay coil 61A,causing the contact 61B to close. The auxiliary winding 7B obtainsstart-up torque from the current phase difference between itself and theprimary winding 7A produced by the operating capacitor 47 and thestart-up capacitors 48 and 48 connected in parallel, thus causing thesynchronous induction motor 2 to start running. After the synchronousinduction motor 2 is energized and starts running, the contact 61B opensafter a while to isolate the start-up capacitors 48 and 48, and thesynchronous induction motor 2 continues steady operation from thecurrent phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47. The runningsynchronous induction motor 2 operates the hermetic electric compressorC, thus enabling an air conditioner to effect air conditioning in theroom wherein the air conditioner is installed, or enabling therefrigerator to effect cooling therein.

[0230] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and the compressor 3 becomes hot.As the compressor 3 becomes hot, the temperature of the stator winding 7rises accordingly. This causes the resistance value of the thermistor 46to change, and the temperature rise in the stator winding 7 is detected.If the detected temperature is higher than a preset temperature level,then the controller 62 detects that the temperature of the statorwinding 7 is higher than the preset level, and passes current throughthe control relay coil 49A to open the control relay contact 49B therebyto cut off the supply of power to the stator winding 7. With thisarrangement, the supply of power to the stator winding 7 can beinterrupted before the stator winding 7 generates abnormal heat whilethe hermetic electric compressor C is in operation, thus making itpossible to securely restrain damage to the stator winding 7 and thethermal demagnetization of the permanent magnets 31. The controller 62causes current to the control relay coil 49A to open the control relaycontact 49B so as to interrupt the supply of power to the stator winding7 if it detects that the temperature of the stator winding 7 is higherthan a preset temperature. Alternatively, however, the controller 62 maycontrol the supply of power to the synchronous induction motor 2 toreduce the number of revolutions thereof or to shut off the supply ofpower to the synchronous induction motor 2 if the temperature of thehermetic electric compressor C rises and exceeds a preset temperaturelevel.

[0231] Furthermore, if large current flows into the stator winding 7 dueto overloaded operation of the hermetic electric compressor C, the linecurrent detector 63 detects the large current flow. If the detectedcurrent is larger than a preset current level, then the controller 62detects the large current flow into the stator winding 7, and passescurrent through the control relay coil 49A to open the control relaycontact 49B so as to cut off the supply of power to the stator winding7. With this arrangement, the supply of power to the stator winding 7can be interrupted so as to protect the synchronous induction motor 2before an overloaded operation of the hermetic electric compressor C iscontinued, which would lead to damage to the hermetic electriccompressor C. The controller 62 shuts off the supply of power to thestator winding 7 to protect the synchronous induction motor 2 inresponse to a signal issued by the thermistor 46 or the line currentdetector 63, whichever issued the detection signal first.

[0232]FIG. 55 is a longitudinal sectional side view of a part of anotherhermetic electric compressor C (the part being in the vicinity of an endcap 1B). The hermetic electric compressor C shown in FIG. 55 is equippedwith a bimetal switch 64 as a thermal protector that opens and closes acontact at a predetermined temperature. The bimetal switch 64 is securedto the stator winding 7 by a polyester yarn 70 for binding a coil end ofthe stator winding 7. The bimetal switch 64 is connected between ahermetic terminal 25 provided on the end cap 1B of the hermetic vessel 1and the stator winding 7, and it cuts off the supply of power from thesingle-phase alternating current commercial power source AC to thestator winding 7 by opening the contact 61B if the temperature of thestator winding 7 exceeds a predetermined temperature level.

[0233]FIG. 56 is an electrical circuit diagram of the synchronousinduction motor 2 of the hermetic electric compressor C shown in FIG.55. Referring to FIG. 56, the synchronous induction motor 2, whichreceives power from a single-phase alternating current commercial powersource AC through the intermediary of the bimetal switch 64, is equippedwith a stator winding 7 formed of a primary winding 7A and an auxiliarywinding 7B. One end of the primary winding 7A is connected to one end ofthe single-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source AC.One end of the auxiliary winding 7B is connected to one end of thesingle-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source ACthrough the intermediary of an operating capacitor 47.

[0234] One end of the auxiliary winding 7B is also connected to theother end of the single-phase alternating current commercial powersource AC through the intermediary of a contact 61B of a start-up relay61 and start-up capacitors 48 and 48. These contact 61B and the start-upcapacitors 48 and 48 are connected in series, and the operatingcapacitor 47 is connected in parallel to the contact 61B and thestart-up capacitors 48 and 48. The operating capacitor 47 is set to acapacitance suited for steady operation. In the state wherein theoperating capacitor 47 and the start-up capacitors 48 and 48 areconnected in parallel, the capacitors 47, 48, and 48 are set tocapacitances suited for start-up. Reference numerals 48A and 48A denotedischarge resistors for discharging currents charged in the start-upcapacitors 48 and 48, and reference numeral 61A denotes a start-up relaycoil.

[0235] When the power switch PSW is turned ON, current is supplied fromthe single-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B. At the start-up of thesynchronous induction motor 2, current passes through the start relaycoil 61A, causing the contact 61B to close. The auxiliary winding 7Bobtains start-up torque from the current phase difference between itselfand the primary winding 7A produced by the operating capacitor 47 andthe start-up capacitors 48 and 48 connected in parallel, thus causingthe synchronous induction motor 2 to start running. After thesynchronous induction motor 2 is energized and starts running, thecontact 61B opens after a while to isolate the start-up capacitors 48and 48, and the synchronous induction motor 2 continues steady operationfrom the current phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47. The runningsynchronous induction motor 2 operates the hermetic electric compressorC, thus enabling an air conditioner to effect air conditioning in theroom wherein the air conditioner is installed, or the refrigerator toeffect cooling therein.

[0236] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and the compressor 3 becomes hot.As the compressor 3 becomes hot, the temperature of the stator winding 7rises accordingly. The bimetal switch 64 detects the temperature of thestator winding 7. If the detected temperature is higher than a presettemperature level, then the bimetal switch 64 opens the contact tointerrupt the supply of power to the stator winding 7. With thisarrangement, the supply of power to the stator winding 7 can beinterrupted before the stator winding 7 generates abnormal heat whilethe hermetic electric compressor C is in operation, thus making itpossible to securely restrain damage to the stator winding 7 and thethermal demagnetization of the permanent magnets 31 and to protect thehermetic electric compressor C from damage due to abnormal heatgeneration.

[0237]FIG. 57 is a longitudinal sectional side view of a part of anotherhermetic electric compressor C (the part being in the vicinity of an endcap 1B). The hermetic electric compressor C shown in FIG. 57 is equippedwith a bimetal switch 64 as a thermal protector that opens and closes acontact at a predetermined temperature, as mentioned above. The bimetalswitch 64 is directly connected to a hermetic terminal 25 that extendsinto a hermetic vessel 1. The bimetal switch 64 is connected between thehermetic terminal 25 provided on the end cap 1B of the hermetic vessel 1and the stator winding 7, and it cuts off the supply of power from thesingle-phase alternating current commercial power source AC to thestator winding 7 by opening the contact if the temperature in thehermetic vessel 1 exceeds a predetermined temperature level. Theelectrical circuit diagram of the hermetic electric compressor C is thesame as that shown in FIG. 56.

[0238] When the power switch PSW is turned ON, current is supplied fromthe single-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B. At the start-up of thesynchronous induction motor 2, current passes through the start relaycoil 61A, causing the contact 61B to close. The auxiliary winding 7Bobtains start-up torque from the current phase difference between itselfand the primary winding 7A produced by the operating capacitor 47 andthe start-up capacitors 48 and 48 connected in parallel, thus causingthe synchronous induction motor 2 to start running. After thesynchronous induction motor 2 is energized and starts running, thecontact 61B opens after a while to isolate the start-up capacitors 48and 48, and the synchronous induction motor 2 continues steady operationfrom the current phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47. The runningsynchronous induction motor 2 operates the hermetic electric compressorC, thus enabling an air conditioner to effect air conditioning in theroom wherein the air conditioner is installed, or the refrigerator toeffect cooling therein.

[0239] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and becomes hot. As the compressor3 becomes hot, the temperature of the stator winding 7 rises, and thetemperature inside the end cap 1B also rises accordingly. As thetemperature inside the end cap 1B rises, the bimetal switch 64 detectsthe temperature. If the detected temperature inside the end cap 1B ishigher than a preset temperature level, then the contact is opened tointerrupt the supply of power to the stator winding 7. With thisarrangement, the supply of power to the stator winding 7 can beinterrupted before the stator 4 or the stator winding 7 generatesabnormal heat while the hermetic electric compressor C is in operation,thus making it possible to securely restrain damage to the statorwinding 7 and the thermal demagnetization of the permanent magnets 31and to protect the hermetic electric compressor C from damage due toabnormal heat generation.

[0240]FIG. 58 is a longitudinal sectional side view of a part of yetanother hermetic electric compressor C (the part being in the vicinityof an end cap 1B). The hermetic electric compressor C shown in FIG. 58is equipped with a thermostat 65 as a thermal protector that opens andcloses a contact at a predetermined temperature. The thermostat 65 isconnected to a connecting terminal 71 provided on the end cap 1B of ahermetic vessel 1 by a lead wire 72, and it cuts off the supply of powerfrom the single-phase alternating current commercial power source AC tothe stator winding 7 by opening the contact if the temperature in thehermetic vessel 1 exceeds a predetermined temperature level.

[0241]FIG. 59 shows an electrical circuit diagram of the synchronousinduction motor 2 of the hermetic electric compressor C shown in FIG.58. Referring to FIG. 59, reference numeral 65 denotes the thermostat.The rest of FIG. 59 is the same as FIG. 54. When a power switch PSW isturned ON with a control relay contact 49B closed, current is suppliedfrom the single-phase alternating current commercial power source AC tothe primary winding 7A and the auxiliary winding 7B. At the start-up ofthe synchronous induction motor 2, current passes through a start relaycoil 61A, causing the contact 61B to close. The auxiliary winding 7Bobtains start-up torque from the current phase difference between itselfand the primary winding 7A produced by the operating capacitor 47 andthe start-up capacitors 48 and 48 connected in parallel thereto, thuscausing the synchronous induction motor 2 to start running. After thesynchronous induction motor 2 is energized and starts running, thecontact 61B opens after a while to isolate the start-up capacitors 48and 48, and the synchronous induction motor 2 continues steady operationfrom the current phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47. The runningsynchronous induction motor 2 operates the hermetic electric compressorC, thus enabling an air conditioner to effect air conditioning in theroom wherein the air conditioner is installed, or enabling therefrigerator to effect cooling therein.

[0242] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and the compressor 3 becomes hot.As the compressor 3 becomes hot, the temperature inside the end cap 1Balso rises. This causes the thermostat 65 to detect the temperatureinside the end cap 1B, and if the detected temperature is higher than apreset temperature level, the contact thereof is closed. The moment thecontact of the thermostat 65 is closed, the controller 62 causes currentto pass through the control relay coil 49A to open the control relaycontact 49B thereby to cut off the supply of power to the stator winding7. With this arrangement, the supply of power to the stator winding 7can be interrupted before abnormal heat is generated inside the end cap1B while the hermetic electric compressor C is in operation, thus makingit possible to securely restrain damage to the stator winding 7 and thethermal demagnetization of the permanent magnets 31.

[0243] Furthermore, if large current flows into the stator winding 7 dueto overloaded operation of the hermetic electric compressor C, the linecurrent detector 63 detects the large current flow. If the detectedcurrent is larger than a preset current level, then the controller 62detects the large current flow into the stator winding 7, and passescurrent through the control relay-coil 49A to open the control relaycontact 49B to cut off the supply of power to the stator winding 7. Withthis arrangement, the supply of power to the stator winding 7 can beinterrupted so as to protect the synchronous induction motor 2 before anoverloaded operation of the hermetic electric compressor C is continued,which would lead to damage to the hermetic electric compressor C. Thecontroller 62 shuts off the supply of power to the stator winding 7 toprotect the synchronous induction motor 2 in response to a signal issuedby the thermostat 65 or the line current detector 63, whichever issuedthe detection signal first.

[0244]FIG. 60 is a longitudinal sectional side view of a part of afurther hermetic electric compressor C (the part being in the vicinityof an end cap 1B). The hermetic electric compressor C shown in FIG. 60is provided with a thermostat 65 whose resistance value changes withtemperature. The thermostat 65 is secured to the stator winding 7 by apolyester yarn 70 for binding a coil end of the stator winding 7. Thethermostat 65 is connected, by a lead wire 72, also to a connectingterminal 71 provided on the end cap 1B of the hermetic vessel 1.

[0245]FIG. 61 is an electrical circuit diagram of the synchronousinduction motor 2 of the hermetic electric compressor C shown in FIG.60. Referring to FIG. 61, the synchronous induction motor 2, whichreceives power from a single-phase alternating current commercial powersource AC is equipped with a stator winding 7 formed of a primarywinding 7A and an auxiliary winding 7B. One end of the primary winding7A is connected to one end of the single-phase alternating currentcommercial power source AC, and the other end thereof is connected tothe other end of the power source AC. One end of the auxiliary winding7B is connected to one end of the single-phase alternating currentcommercial power source AC, and the other end thereof is connected tothe other end of the power source AC through the intermediary of anoperating capacitor 47.

[0246] One end of the auxiliary winding 7B is also connected to theother end of the single-phase alternating current commercial powersource AC through the intermediary of a contact 61B of a start-up relay61 and start-up capacitors 48 and 48. These contact 61B and the start-upcapacitors 48 and 48 are connected in series, and the operatingcapacitor 47 is connected in parallel to the contact 61B and thestart-up capacitors 48 and 48. The operating capacitor 47 is set to acapacitance suited for steady operation. In the state wherein theoperating capacitor 47 and the start-up capacitors 48 and 48 areconnected in parallel, the capacitors 47, 48, and 48 are set tocapacitances suited for start-up. Reference numerals 48A and 48A denotedischarge resistors for discharging currents charged in the start-upcapacitors 48 and 48, reference numeral 61A denotes a start-up relaycoil, and PSW denotes a power switch.

[0247] A control relay 49 is provided that is connected between thepower switch PSW and the stator winding 7 and that serves also as aprotective switch for supplying power from the single-phase alternatingcurrent commercial power source AC to the stator winding 7 and to cutoff the supply of power to the stator winding 7. One end of thethermostat 65 secured to the stator winding 7 is connected to one end ofthe single-phase alternating current commercial power source AC throughthe intermediary of a relay coil 49A of the control relay 49 and anoverload switch 73 functioning as an overload protector. The other endof the thermostat 65 is connected to the other end of the single-phasealternating current commercial power source AC. Reference numeral 49Bdenotes switch contacts that cause current to pass through a controlrelay coil 49A so as to open the control relay 49 if a predeterminedoverload current flows into the overload switch 73.

[0248] When the power switch PSW is turned ON with the control relaycontact 49B closed, current is supplied from the single-phasealternating current commercial power source AC to the primary winding 7Aand the auxiliary winding 7B through the intermediary of an overloadswitch 73 and the control relay contact 49B. At the start-up of thesynchronous induction motor 2, current passes through a start relay coil61A, causing the contact 61B to close. The auxiliary winding 7B obtainsstart-up torque from the current phase difference between itself and theprimary winding 7A produced by the operating capacitor 47 and thestart-up capacitors 48 and 48 connected in parallel, thus causing thesynchronous induction motor 2 to start running. After the synchronousinduction motor 2 is energized and starts running, the contact 61B opensafter a while to isolate the start-up capacitors 48 and 48, and thesynchronous induction motor 2 continues steady operation from thecurrent phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47. The runningsynchronous induction motor 2 operates the hermetic electric compressorC, thus enabling an air conditioner to effect air conditioning in theroom wherein the air conditioner is installed, or enabling therefrigerator to effect cooling therein.

[0249] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and the compressor 3 becomes hot.As the compressor 3 becomes hot, the temperature of the stator winding 7rises accordingly. The thermostat 65 detects the temperature, and if thedetected temperature is higher than a preset temperature level, then thecontact is closed. This causes current to pass through the control relaycoil 49A to open the control relay contacts 49B thereby to cut off thesupply of power to the stator winding 7. With this arrangement, thesupply of power to the stator winding 7 can be interrupted beforeabnormal heat is generated inside the end cap 1B while the hermeticelectric compressor C is in operation, thus making it possible tosecurely restrain damage to the stator winding 7 and the thermaldemagnetization of the permanent magnets 31.

[0250] If overload current flows into the stator winding 7 due tooverloaded operation of the hermetic electric compressor C, the overloadswitch 73 detects the overload current. If the detected current exceedsa preset current value, then the overload switch 73 passes currentthrough the control relay coil 49A to open the control relay contacts49B so as to cut off the supply of power to the stator winding 7. Thismakes it possible to cut off the supply of power to the stator winding 7to protect the synchronous induction motor 2 before the hermeticelectric compressor C is damaged due to an overloaded operation of thehermetic electric compressor C. The supply of power to the statorwinding 7 is interrupted in order to protect the synchronous inductionmotor 2 in response to a signal issued by the thermostat 65 or theoverload switch 73, whichever issued the detection signal first.

[0251]FIG. 62 is a longitudinal sectional side view of a part of stillanother hermetic electric compressor C (the part being in the vicinityof an end cap 1B). The hermetic electric compressor C shown in FIG. 62is equipped with an overload switch 73 as an overload protector. Theoverload switch 73 is secured to the end cap 1B of a hermetic vessel 1.More specifically, the overload switch 73 is secured to a hermeticterminal 25 on the end surface of the hermetic vessel 1, and opens acontact (not shown) to cut off the supply of power to the stator winding7 if a predetermined overload current passes. Reference numeral 74denotes a cover for protecting the hermetic terminal 25 and the overloadswitch 73, and reference numeral 75 denotes a nut for securing the cover74.

[0252]FIG. 63 is an electrical circuit diagram of the synchronousinduction motor 2 of the hermetic electric compressor C shown in FIG.62. Referring to FIG. 63, the synchronous induction motor 2, whichreceives power from a single-phase alternating current commercial powersource AC through the intermediary of the overload switch 73 is equippedwith a stator winding 7 formed of a primary winding 7A and an auxiliarywinding 7B. One end of the primary winding 7A is connected to one end ofthe single-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source AC.One end of the auxiliary winding 7B is connected to one end of thesingle-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source ACthrough the intermediary of an operating capacitor 47.

[0253] One end of the auxiliary winding 7B is also connected to theother end of the single-phase alternating current commercial powersource AC through the intermediary of a contact 61B of a start-up relay61 and a start-up capacitor 48. These contact 61B and the start-upcapacitor 48 are connected in series, and the operating capacitor 47 isconnected in parallel to the contact 61B and the start-up capacitor 48.The operating capacitor 47 is set to a capacitance suited for steadyoperation. In the state wherein the operating capacitor 47 and thestart-up capacitor 48 are connected in parallel, the capacitors 47 and48 are set to capacitances suited for start-up. Reference numeral 48Adenotes a discharge resistor for discharging current charged in thestart-up capacitor 48, reference numeral 61A denotes a start-up relaycoil, and PSW denotes a power switch.

[0254] When the power switch PSW is turned ON, current is supplied fromthe single-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B through the intermediaryof the overload switch 73. At the start-up of the synchronous inductionmotor 2, current passes through a start relay coil 61A, causing thecontact 61B to close. The auxiliary winding 7B obtains start-up torquefrom the current phase difference from the primary winding 7A producedby the operating capacitor 47 and the start-up capacitor 48 connected inparallel thereto, thus causing the synchronous induction motor 2 tostart running. After the synchronous induction motor 2 is energized andstarts running, the contact 61B opens after a while to isolate thestart-up capacitor 48, and the synchronous induction motor 2 continuessteady operation from the current phase difference between the primarywinding 7A and the auxiliary winding 7B produced by the operatingcapacitor 47. The running synchronous induction motor 2 operates thehermetic electric compressor C, thus enabling an air conditioner toeffect air conditioning in the room wherein the air conditioner isinstalled, or enabling the refrigerator to effect cooling therein.

[0255] If overload current flows into the stator winding 7 due tooverloaded operation of the hermetic electric compressor C, the overloadswitch 73 detects the overload current. If the detected current exceedsa preset current value, then the overload switch 73 causes the contactto open so as to cut off the supply of power to the stator winding 7.More specifically, if overload current flows into the stator winding 7,then the overload switch 73 opens the contact thereby to interrupt thesupply of power from the single-phase alternating current commercialpower source AC to the stator winding 7. This makes it possible to cutoff the supply of power to the stator winding 7 to protect thesynchronous induction motor 2 before the hermetic electric compressor Cis damaged due to an overloaded operation of the hermetic electriccompressor C.

[0256]FIG. 64 is a longitudinal sectional side view of a part of stillanother hermetic electric compressor C (the part being in the vicinityof an end cap 1B). The hermetic electric compressor C shown in FIG. 64is equipped with a thermostat 65 functioning as an overload protectorthat opens/closes a contact at a predetermined temperature. Thethermostat 65 is secured to the end cap 1B, which is an outer surface ofa hermetic vessel 1. More specifically, the thermostat 65 is secured tothe a hermetic terminal 25 on the end surface of the hermetic vessel 1,and opens/closes a contact according to the temperature of the end cap1B. Reference numeral 74 denotes a cover for protecting the hermeticterminal 25 and the thermostat 65, and reference numeral 75 denotes anut for securing the cover 74.

[0257]FIG. 65 is an electrical circuit diagram of the synchronousinduction motor 2 of the hermetic electric compressor C shown in FIG.64. Referring to FIG. 65, the synchronous induction motor 2, whichreceives power from a single-phase alternating current commercial powersource AC through the intermediary of the overload switch 73 and thethermostat 65 is equipped with a stator winding 7 formed of a primarywinding 7A and an auxiliary winding 7B. One end of the primary winding7A is connected to one end of the single-phase alternating currentcommercial power source AC, and the other end thereof is connected tothe other end of the power source AC. One end of the auxiliary winding7B is connected to one end of the single-phase alternating currentcommercial power source AC, and the other end thereof is connected tothe other end of the power source AC through the intermediary of anoperating capacitor 47.

[0258] One end of the auxiliary winding 7B is also connected to theother end of the single-phase alternating current commercial powersource AC through the intermediary of a contact 61B of a start-up relay61 and a start-up capacitor 48. These contact 61B and the start-upcapacitor 48 are connected in series, and the operating capacitor 47 isconnected in parallel to the contact 61B and the start-up capacitor 48.The operating capacitor 47 is set to a capacitance suited for steadyoperation. In the state wherein the operating capacitor 47 and thestart-up capacitor 48 are connected in parallel, the capacitors 47 and48 are set to capacitances suited for start-up. Reference numeral 48Adenotes a discharge resistor for discharging current charged in thestart-up capacitor 48, reference numeral 61A denotes a start-up relaycoil, and PSW denotes a power switch.

[0259] When the power switch PSW is turned ON, current is supplied fromthe single-phase alternating current commercial power source AC to theprimary winding 7A and the auxiliary winding 7B. At the start-up of thesynchronous induction motor 2, current passes through the start relaycoil 61A, causing the contact 61B to close. The auxiliary winding 7Bobtains start-up torque from the current phase difference between itselfand the primary winding 7A produced by the operating capacitor 47 andthe start-up capacitor 48 connected in parallel thereto, thus causingthe synchronous induction motor 2 to start running. After thesynchronous induction motor 2 is energized and starts running, thecontact 61B opens after a while to isolate the start-up capacitor 48,and the synchronous induction motor 2 continues steady operation fromthe current phase difference between the primary winding 7A and theauxiliary winding 7B produced by the operating capacitor 47. The runningsynchronous induction motor 2 operates the hermetic electric compressorC, thus enabling an air conditioner to effect air conditioning in theroom wherein the air conditioner is installed, or enabling therefrigerator to effect cooling therein.

[0260] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and the compressor 3 becomes hot.As the compressor 3 becomes hot, the temperature of the end cap 1B risesaccordingly. The thermostat 65 detects the temperature of the end cap1B, and if the temperature of the end cap 1B is higher than a presettemperature level, then the contact is opened. This interrupts thesupply of power to the stator winding 7. With this arrangement, thesupply of power to the stator winding 7 can be shut off before abnormalheat is generated inside the end cap 1B while the hermetic electriccompressor C is in operation, thus making it possible to securelyrestrain damage to the stator winding 7 and the thermal demagnetizationof the permanent magnets 31.

[0261] If overload current flows into the stator winding 7 due tooverloaded operation of the hermetic electric compressor C, the overloadswitch 73 detects the overload current. If the detected current exceedsa preset current value, then the overload switch 73 opens the contact soas to cut off the supply of power to the stator winding 7. This makes itpossible to cut off the supply of power to the stator winding 7 toprotect the synchronous induction motor 2 before the hermetic electriccompressor C is damaged due to an overloaded operation of the hermeticelectric compressor C. The supply of power to the stator winding 7 isinterrupted in order to protect the synchronous induction motor 2 inresponse to a signal issued by the thermostat 65 or the overload switch73, whichever issued the detection signal first.

[0262]FIG. 66 is an electrical circuit diagram of another synchronousinduction motor 2 of the hermetic electric compressor C. A thermostat 65is secured to the outer surface of the hermetic vessel 1, as in the caseof the compressor shown in FIG. 64. Referring to FIG. 66, thesynchronous induction motor 2, which receives power from a single-phasealternating current commercial power source AC is equipped with a statorwinding 7 formed of a primary winding 7A and an auxiliary winding 7B.One end of the primary winding 7A is connected to one end of thesingle-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source AC.One end of the auxiliary winding 7B is connected to one end of thesingle-phase alternating current commercial power source AC, and theother end thereof is connected to the other end of the power source ACthrough the intermediary of an operating capacitor 47. The operatingcapacitor 47 is set to a capacitance suited for start-up and steadyoperation of the synchronous induction motor 2.

[0263] A control relay 49 is provided which is connected between thepower switch PSW and the stator winding 7 and which acts also as aprotective switch for supplying power from the single-phase alternatingcurrent commercial power source AC to the stator winding 7 and forcutting off the supply of power to the stator winding 7. A controller 62is connected to the thermostat 65 secured to the end cap 1B and alsoconnected to a control relay coil 49A of the control relay 49. Connectedto the controller 62 is a current-sensitive line current detector 63that is connected to one end of the single-phase alternating currentcommercial power source AC and that functions as an overload protectorfor detecting line current. Reference numeral 49B denotes a controlrelay contact.

[0264] When the power switch PSW is turned ON to supply power from thesingle-phase alternating current commercial power source AC to thestator winding 7, a parallel circuit of the operating capacitor 47 andthe primary winding 7A is connected to the auxiliary winding 7B. Theauxiliary winding 7B obtains start-up operating torque produced by thecurrent phase difference between the primary winding 7A and theauxiliary winding 7B, thus causing the synchronous induction motor 2 tostart running. The synchronous induction motor 2 then shifts to thesteady operation from the current phase difference between the primarywinding 7A and the auxiliary winding 7B produced by the operatingcapacitor 47. In this case, the operating capacitor 47 serves also as astart-up capacitor.

[0265] As the hermetic electric compressor C is operated, thetemperature of the compressor 3 rises and the compressor 3 becomes hot.As the compressor 3 becomes hot, the temperature of the end cap 1B (theouter surface of the hermetic vessel 1) rises accordingly. Thethermostat 65 detects the temperature of the outer surface of thehermetic vessel 1, and if the detected temperature is higher than apreset temperature level, then the contact is closed. This causes thecontroller 62 to detect that the temperature of the outer surface of thehermetic vessel 1 is higher than the preset temperature and to passcurrent through the control relay coil 49A to open the control relaycontact 49B thereby to cut off the supply of power to the stator winding7. With this arrangement, the supply of power to the stator winding 7can be interrupted before the hermetic vessel 1 develops abnormal heatwhile the hermetic electric compressor C is in operation, thus making itpossible to securely restrain damage to the stator winding 7 and thethermal demagnetization of the permanent magnets 31.

[0266] Furthermore, if large current flows into the stator winding 7 dueto an overloaded operation of the hermetic electric compressor C, theline current detector 63 detects the large current flow. If the detectedcurrent is larger than a preset current level, then the controller 62passes current through the control relay coil 49A to open the controlrelay contact 49B so as to cut off the supply of power to the statorwinding 7. With this arrangement, the supply of power to the statorwinding 7 can be interrupted so as to protect the synchronous inductionmotor 2 before an overloaded operation of the hermetic electriccompressor C is continued, which would lead to damage to the statorwinding 7. The controller 62 shuts off the supply of power to the statorwinding 7 to protect the synchronous induction motor 2 in response to asignal issued by the thermostat 65 or the line current detector 63,whichever issued the detection signal first.

[0267] The controller 62 incorporates a timer. The controller 62 isadapted to restart the supply of current to the synchronous inductionmotor 2 after waiting for the elapse of a predetermined delay time sincethe supply of current to the synchronous induction motor 2 was cut off.This means that the controller 62 waits for the predetermined timecounted by the timer before it restarts the supply of current to thesynchronous induction motor 2 after the supply of current to thesynchronous induction motor 2 was cut off. Thus, since the predetermineddelay time is allowed before the supply of power to the synchronousinduction motor 2 is restarted after the power to the synchronousinduction motor was cut off, it is possible to restrain the rotor 5 frombecoming hot due to, for example, frequent repetition of energizing andde-energizing of the synchronous induction motor 2 because of a startingfailure of the synchronous induction motor 2. This arrangement make italso possible to restrain the demagnetization of the permanent magnets31 embedded in the rotor 5 caused by the heat generated in the rotor 5.

[0268] As described above, the hermetic electric compressor C isprovided with the thermal protector (the thermistor 46, the bimetalswitch 64, or the thermostat 65) to cut off the supply of power to thesynchronous induction motor 2 in response to a predetermined temperaturerise. Hence, the supply of power to the stator winding 7 can beinterrupted before the stator winding 7 generates abnormal heat whilethe hermetic electric compressor C is running. This arrangement makes itpossible to restrain the demagnetization of the permanent magnets 31embedded in the rotor yoke 5A caused by a temperature rise, permittingdramatically improved reliability of the hermetic electric compressor C.

[0269] Moreover, the hermetic electric compressor C is provided with theoverload protector (the line current detector 63 or the overload switch73) to cut off the supply of power to the synchronous induction motor 2in response to a predetermined overload current. Hence, the supply ofpower to the synchronous induction motor 2 to restrain a temperaturerise in the synchronous induction motor 2 thereby to protect it if thehermetic electric compressor C is operated under an overload. This makesit possible to prevent damage to the synchronous induction motor 2,permitting a markedly prolonged service life of the synchronousinduction motor 2 with resultant markedly improved reliability of thehermetic electric compressor C.

[0270] In the embodiments, the stainless steel plates have been used forthe end surface members 66 and 67 holding the permanent magnets 31.Alternatively, however, using aluminum plates that allow further easierpassage of current for the end surface members 66 and 67 will permit areduction in the secondary resistance, leading to significantly higheroperational performance.

[0271] In the embodiments, the rotary compressor has been used as anexample of the hermetic electric compressor C; however, the presentinvention is not limited thereto. The present invention may be alsoeffectively applied to a hermetic scroll compressor constituted by apair of meshed scrolls.

[0272] As described above in detail, according to the present invention,the synchronous induction motor includes a stator equipped with a statorwinding, a rotor rotating in the stator, a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting, end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting, permanent magnets inserted in slots formed such that theypenetrate the rotor yoke, and a pair of end surface members formed of anon-magnetic material that closes the openings of both ends of theslots, wherein one of the end surface members is secured to the rotoryoke by one of the end rings when the secondary conductors and end ringsare formed, and the other end surface member is secured to the rotoryoke by a fixture. Therefore, one of the end surface members can besecured to the rotor yoke at the same time when the secondary conductorsand the end rings are die-cast.

[0273] With this arrangement, after the permanent magnets are insertedinto the slots, the permanent magnets can be secured to the rotor merelyby securing the other end surface member to the rotor yoke by a fixture.It is therefore possible to reduce the number of steps for installingthe permanent magnets and to improve the assemblability, permitting theoverall productivity of synchronous induction motors to be dramaticallyimproved.

[0274] Furthermore, according to the present invention, the synchronousinduction motor includes a stator equipped with a stator winding, arotor rotating in the stator, a plurality of secondary conductors whichis positioned around a rotor yoke constituting the rotor and which isformed by die casting, end rings which are positioned on the peripheralportions of both end surfaces of the rotor yoke and which are integrallyformed with the secondary conductors by die casting, permanent magnetsinserted in slots formed such that they penetrate the rotor yoke, and apair of end surface members formed of a non-magnetic material thatcloses the openings of both ends of the slots, wherein a non-magneticmember is disposed in contact with the inner sides of the two end ringsto secure the two end surface members by pressing them against the rotoryoke by the non-magnetic member. It is therefore possible to increasethe sectional areas of the end rings by the amount provided by pressingthe end surface members against rotor yoke by the non-magnetic member.With this arrangement, the secondary resistance is decreased by theamount equivalent to the increase in the sectional areas of the endrings. Hence, the loss of the rotor can be decreased and the heatgeneration can be restrained, and the magnetic forces of the magnets canbe effectively used, making it possible to significantly improve therunning performance of the synchronous induction motor.

[0275] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor rotatingin the stator, a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting, end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting, permanent magnets inserted inslots formed such that they penetrate the rotor yoke, and a pair of endsurface members formed of a non-magnetic material that closes theopenings of both ends of the slots, wherein a balancer formed into apredetermined shape beforehand is secured by a fixture to the rotor yoketogether with the end surface member. Therefore, the ease ofinstallation of the balancer can be considerably improved. With thisarrangement, it is no longer necessary to secure the permanent magnetsand the balancer separately, with consequent greater ease ofinstallation. This permits dramatically improved productivity of thesynchronous induction motor.

[0276] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor rotatingin the stator, a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting, end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting, permanent magnets inserted inslots formed such that they penetrate the rotor yoke, and a pair of endsurface members which is formed of a non-magnetic material and whichcloses the openings of both ends of the slots, wherein a plurality oflaminated sheet balancers is secured by a fixture to the rotor yoketogether with the end surface member. Therefore, the ease ofinstallation of the balancer is improved, permitting dramaticallyimproved productivity to be achieved. Furthermore, since a plurality ofsheet balancers is laminated, using inexpensive metal sheets for thebalancer allows a considerable reduction in the cost of the balancer.This leads to a dramatically reduced production cost of the synchronousinduction motor.

[0277] According to the present invention, the synchronous inductionmotor is provided with a stator equipped with a stator winding, a rotorrotating in the stator, a plurality of secondary conductors which ispositioned around a rotor yoke constituting the rotor and which isformed by die casting, end rings which are positioned on the peripheralportions of both end surfaces of the rotor yoke and which are integrallyformed with the secondary conductors by die casting, permanent magnetsinserted in slots formed such that they penetrate the rotor yoke, and apair of end surface members formed of a non-magnetic material thatcloses the openings of both ends of the slots, wherein at least one ofthe end surface members and a balancer are formed into one piece. Hence,the number of components can be reduced. This permits simplerinstallation of the end surface members, resulting in dramaticallyimproved productivity.

[0278] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor rotatingin the stator, a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting, end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting, permanent magnets inserted inslots formed such that they penetrate the rotor yoke, a pair of endsurface members formed of a non-magnetic material that closes theopenings of both ends of the slots, and a balancer secured by beingpress-fitted to the inner side of at least one of the end rings. Hence,the installation of the balancer can be simplified. This arrangementmakes it possible to significantly improve the productivity of thesynchronous induction motor.

[0279] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor rotatingin the stator, a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting, end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting, permanent magnets inserted inslots formed such that they penetrate the rotor yoke, and a pair of endsurface members formed of a non-magnetic material that closes theopenings of both ends of the slots in which the permanent magnets havebeen inserted, wherein the two end surface members are secured to therotor yoke by the two end rings when the secondary conductors and theend rings are formed. This arrangement makes it possible to obviate theneed of, for example, the cumbersome step for inserting the permanentmagnets into the slots, then attaching the end surface members to bothends of the rotor yoke after die-casting the end rings, as in the caseof a prior art. Thus, the productivity of the rotor can be dramaticallyimproved.

[0280] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor which issecured to a rotating shaft and which rotates in the stator, a secondaryconductor provided around the rotor yoke constituting the rotor, and apermanent magnet embedded in the rotor yoke, wherein a magnetic fieldproduced by the permanent magnet does not pass through the rotatingshaft. Thus, it is possible to prevent the rotating shaft from beingmagnetized. This arrangement makes it possible to prevent iron powder orthe like from adhering to the rotating shaft and to protect the rotatingshaft and a bearing from being worn due to the friction attributable tothe magnetic force of the permanent magnet. This permits secureprevention of damage to the motor caused by the friction.

[0281] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor which issecured to a rotating shaft and which rotates in the stator, a secondaryconductor provided around the rotor yoke constituting the rotor, and apermanent magnet embedded in the rotor yoke, wherein a magnetic fieldproduced by the permanent magnet bypasses the rotating shaft. Thus, itis possible to prevent the rotating shaft from being magnetized. Thisarrangement makes it possible to prevent iron powder or the like fromadhering to the rotating shaft and to protect the rotating shaft and abearing from being worn due to the friction attributable to the magneticforce of the permanent magnet. This permits secure prevention of damageto the motor caused by the friction.

[0282] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor which issecured to a rotating shaft and which rotates in the stator, a secondaryconductor provided around the rotor yoke constituting the rotor, and apermanent magnet embedded in the rotor yoke, wherein a magnetic fieldproduced by the permanent magnet passes through only the rotor yoke,excluding the rotating shaft. Thus, it is possible to prevent therotating shaft from being magnetized. This arrangement makes it possibleto prevent iron powder or the like from adhering to the rotating shaftand to protect the rotating shaft and a bearing from being worn due tothe friction attributable to the magnetic force of the permanent magnet.This permits secure prevention of damage to the motor caused by thefriction.

[0283] In the synchronous induction motor in accordance with the presentinvention, a void is formed in the rotor yoke between the permanentmagnet and the rotating shaft, so that the passage of the magnetic fieldproduced by the permanent magnet can be reduced. Thus, it is possible toprevent the rotating shaft from being magnetized. This arrangement makesit possible to prevent iron powder or the like from adhering to therotating shaft and to protect the rotating shaft and a bearing frombeing worn due to the friction attributable to the magnetic force of thepermanent magnet. This permits secure prevention of damage to the motorcaused by the friction.

[0284] In the synchronous induction motor in accordance with the presentinvention, a pair of the permanent magnets is disposed, sandwiching therotating shaft therebetween, and permanent magnets for attracting themagnetic field produced by the paired permanent magnets are disposed atboth ends of a line that passes the paired permanent magnets and therotating shaft. It is therefore possible to prevent the magnetic fieldproduced by the paired permanent magnets from passing through therotating shaft. Thus, it is possible to prevent the rotating shaft frombeing magnetized. This arrangement makes it possible to prevent ironpowder or the like from adhering to the rotating shaft and to protectthe rotating shaft and a bearing from being worn due to the frictionattributable to the magnetic force of the permanent magnet. This permitssecure prevention of damage to the motor caused by the friction.

[0285] In the synchronous induction motor in accordance with the presentinvention, the permanent magnets are provided at both ends of a linethat connects two magnetic poles, and the permanent magnets are radiallydisposed substantially about the rotating shaft. Hence, the magneticfield produced by the permanent magnets can be spaced away from therotating shaft. Thus, it is possible to prevent the rotating shaft frombeing magnetized. This arrangement makes it possible to prevent ironpowder or the like from adhering to the rotating shaft and to protectthe rotating shaft and a bearing from being worn due to the frictionattributable to the magnetic force of the permanent magnet. This permitssecure prevention of damage to the motor due to the friction.

[0286] According to the present invention, the synchronous inductionmotor includes a stator equipped with a stator winding, a rotor rotatingin the stator, a secondary conductor provided around the rotor yokeconstituting the rotor, and a permanent magnet embedded in the rotoryoke, wherein the permanent magnet is magnetized by current passedthrough the stator winding. Hence, for example, a rotor in which amagnetic material for the permanent magnet that has not yet beenmagnetized has been inserted is installed in the stator, so that therotor can be inserted into the stator without being magneticallyattracted to its surrounding. This arrangement makes it possible toprevent inconvenience of lower productivity of the synchronous inductionmotor, thus permitting improved assemblability of the synchronousinduction motor. This allows a synchronous induction motor with highreliability to be provided.

[0287] In the synchronous induction motor in accordance with the presentinvention, the permanent magnet is made of a rare earth type magnet or aferrite magnet, so that high magnet characteristic can be achieved. Withthis arrangement, the magnitude of the current passed through the statorwinding can be reduced so as to control the temperature at the time ofmagnetization to a minimum. Hence, the deformation of the rotor or thestator or the like that would be caused by high temperature can beminimized, making it possible to provide a synchronous induction motorwith secured high quality.

[0288] Especially in the case of a synchronous induction motor, currentpasses through the secondary conductor even during normal synchronousoperation, causing the temperature of the entire rotor to rise.Therefore, a reduction in demagnetization at high temperature can berestrained by using, for example, a ferrite magnet or a rare earth typemagnet (the coercive force at normal temperature being 1350 to 2150 kA/mand the coercive force temperature coefficient being −0.7%/° C. orless).

[0289] In the synchronous induction motor in accordance with the presentinvention, the stator winding is of a single-phase configuration and hasa primary winding and an auxiliary winding, and the permanent magnet ismagnetized by the current passed through either the primary winding orthe auxiliary winding. Hence, it is possible to achieve bettermagnetizing performance than, for example, in the case where current ispassed through both the primary winding and the auxiliary winding at thesame time. This allows an unmagnetized magnet material to be intenselymagnetized.

[0290] In the synchronous induction motor in accordance with the presentinvention, the stator winding is of a three-phase configuration thatincludes a three-phase winding. The permanent magnet is magnetized bycurrent passed through a single phase, two phases, or three phases ofthe stator windings. Therefore, it is possible to select the phase orphases through which current is to be passed according to thedisposition of the magnet or the permissible current (againstdeformation or the like) of the windings.

[0291] In the synchronous induction motor in accordance with the presentinvention, the stator windings are coated with varnish or a stickingagent that is heated to fuse the windings. Hence, for example, even ifthe stator windings generate heat and become hot when an unmagnetizedmagnet material inserted into the rotor is magnetized by passing currentthrough the stator windings, it is possible to restrain the deformationof winding ends of the stator windings and the deterioration of windingfilms caused by the heat. Thus, since the winding ends of the statorwindings do not deform even if an unmagnetized magnet material insertedinto the rotor is magnetized, a highly reliable synchronous inductionmotor can be provided.

[0292] Furthermore, according to the present invention, the synchronousinduction motor in accordance with the present invention is installed ina compressor, allowing the production cost of the compressor to beconsiderably reduced.

[0293] In addition, it is possible to prevent inconveniences in thatiron powder adhere to the rotating shaft of the synchronous inductionmotor of the compressor or the rotating shaft is magnetically attractedto the bearing and wears itself. This makes it possible to prevent theoperation performance of the compressor from degrading.

[0294] Moreover, according to the present invention, the compressor isused with an air conditioner or an electric refrigerator or the like.Hence, the production cost of the air conditioner or the electricrefrigerator can be decreased.

[0295] It is also possible to restrain the degradation of the operationperformance of the air condition or the electric refrigerator or thelike.

[0296] According to the present invention, the manufacturing method fora synchronous induction motor having a stator equipped with a statorwinding, a rotor rotating in the stator, a secondary conductor providedaround a rotor yoke constituting the rotor, and a permanent magnetembedded in the rotor yoke, includes a step for embedding a magnetconstituent for the permanent magnet in the rotor yoke and a step forpassing current through the stator winding to magnetize the magnetconstituent. Hence, the rotor can be inserted into the stator withoutbeing magnetically attracted to its surrounding, permitting dramaticallyimproved assemblability of the synchronous induction motor. This makesit possible to prevent an inconvenience of reduced productivity of thesynchronous induction motor, which permits improved assemblability ofthe synchronous induction motor. As a result, a highly reliablesynchronous induction motor can be provided.

[0297] In the manufacturing method for the synchronous induction motorin accordance with the present invention, a rare earth type or ferritematerial is used for the magnet constituent. Therefore, a high magnetcharacteristic can be achieved even if, for example, a magnetizingmagnetic field is weak. This makes it possible to reduce the currentpassing through the stator winding so as to minimize a temperature risethat occurs at the time of magnetization. Thus, the deformation of therotor or the stator or the like caused by high temperature can beminimized, ensuring high quality of the synchronous induction motor.

[0298] In the manufacturing method for the synchronous induction motorin accordance with the present invention, the stator winding is of asingle-phase configuration and has a primary winding and an auxiliarywinding, and the magnet constituent is magnetized by the current passedthrough either the primary winding or the auxiliary winding. Hence, itis possible to achieve better magnetizing performance than, for example,in the case where current is passed through both the primary winding andthe auxiliary winding at the same time. This allows an unmagnetizedmagnet material to be intensely magnetized.

[0299] In the manufacturing method for the synchronous induction motorin accordance with the present invention, the stator winding is of athree-phase configuration that includes a three-phase winding. Themagnet constituent is magnetized by current passed through a singlephase, two phases, or three phases of the stator windings. Therefore, itis possible to select the phase or phases through which current is to bepassed according to the disposition of the magnet or the permissiblecurrent (against deformation or the like) of the windings.

[0300] In the manufacturing method for the synchronous induction motorin accordance with the present invention, the stator windings are coatedwith varnish or a sticking agent that is heated to fuse the windings.Hence, for example, even if the stator windings are subjected toelectromagnetic forces when an unmagnetized magnet material insertedinto the rotor is magnetized by passing current through the statorwindings, it is possible to restrain the deformation of the windings andthe deterioration of the films of the windings. Thus, since the windingends of the stator windings do not deform even if an unmagnetized magnetmaterial inserted into the rotor is magnetized, a highly reliablesynchronous induction motor can be provided.

[0301] According to the present invention, the drive unit for asynchronous induction motor includes a stator equipped with a statorwinding formed of a primary winding and an auxiliary winding, a rotorrotating in the stator, a secondary conductor provided around a rotoryoke constituting the rotor, a permanent magnet embedded in the rotoryoke, an operating capacitor connected to the auxiliary winding, and aseries circuit of a start-up capacitor and a PTC, which is connected inparallel to the operating capacitor. This arrangement permits largerrunning torque to be provided at starting up the synchronous inductionmotor equipped with the operating capacitor connected to the auxiliarywinding and the series circuit of the start-up capacitor and the PTC,which is connected in parallel to the operating capacitor. This enablesthe power consumed during normal operation to be reduced, making itpossible to provide a drive unit capable of running the synchronousinduction motor with extremely high efficiency. Hence, considerablyhigher efficiency can be achieved during the operation of thesynchronous induction motor.

[0302] According to the present invention, the drive unit for asynchronous induction motor that includes a stator equipped with astator winding formed of a primary winding and an auxiliary winding, arotor rotating in the stator, a secondary conductor provided around arotor yoke constituting the rotor, a permanent magnet embedded in therotor yoke, an operating capacitor connected to the auxiliary winding,and a PTC connected in parallel to the operating capacitor. Thisarrangement permits larger running torque to be provided at starting upthe synchronous induction motor equipped with the operating capacitorconnected to the auxiliary winding and the PTC connected in parallel tothe operating capacitor. This enables the power consumed during normaloperation to be reduced, making it possible to provide a drive unitcapable of running the synchronous induction motor with extremely highefficiency. Hence, considerably higher efficiency can be achieved duringthe operation of the synchronous induction motor.

[0303] According to the present invention, the drive unit for asynchronous induction motor includes a stator equipped with a statorwinding formed of a primary winding and an auxiliary winding, a rotorrotating in the stator, a secondary conductor provided around a rotoryoke constituting the rotor, a permanent magnet embedded in the rotoryoke, an operating capacitor connected to the auxiliary winding, and aseries circuit of a start-up capacitor and a start-up relay contact,which is connected in parallel to the operating capacitor. Thisarrangement permits larger running torque to be provided at starting upthe synchronous induction motor equipped with the operating capacitorconnected to the auxiliary winding and the series circuit of thestart-up capacitor and the start-up relay contact, which is connected inparallel to the operating capacitor. This enables the power consumedduring normal operation to be reduced, making it possible to provide adrive unit capable of running the synchronous induction motor withextremely high efficiency. Hence, considerably higher efficiency can beachieved during the operation of the synchronous induction motor.

[0304] According to the present invention, the drive unit for asynchronous induction motor includes a stator equipped with a statorwinding formed of a primary winding and an auxiliary winding, a rotorrotating in the stator, a secondary conductor provided around a rotoryoke constituting the rotor, a permanent magnet embedded in the rotoryoke, and an operating capacitor connected to the auxiliary winding.This arrangement permits larger running torque to be provided atstarting up the synchronous induction motor equipped with the operatingcapacitor connected to the auxiliary winding. This enables the powerconsumed during normal operation to be reduced, making it possible toprovide a drive unit capable of running the synchronous induction motorwith extremely high efficiency. Hence, considerably higher efficiencycan be achieved during the operation of the synchronous induction motor.

[0305] According to the present invention, the hermetic electriccompressor includes a compression unit and an electric unit for drivingthe compression unit in a hermetic vessel, wherein the electric unit issecured to the hermetic vessel and constituted by a stator equipped witha stator winding and a rotor rotating in the stator, the rotor has asecondary conductor provided around a rotor yoke and a permanent magnetembedded in the rotor yoke, and a thermal protector for cutting off thesupply of current to the electric unit in response to a predeterminedtemperature rise is provided in the hermetic vessel. Therefore,installing the thermal protector onto the stator winding, for example,makes it possible to cut off the supply of current to the electric unitif the temperature of the stator winding rises. This arrangement makesit possible to prevent the permanent magnet embedded in the rotor yokefrom being thermally demagnetized by a rise in temperature of theelectric unit. Hence, the supply of current to the stator winding can becut off before the stator winding generates abnormal heat while thehermetic electric compressor is in operation. This makes it possible tosecurely prevent damage to the stator winding and thermaldemagnetization of the permanent magnet so as to ideally maintain thedriving force of a synchronous induction motor, permitting significantlyimproved reliability of the electric unit.

[0306] According to the present invention, the hermetic electriccompressor has a compression unit and an electric unit for driving thecompression unit in a hermetic vessel, wherein the electric unit issecured to the hermetic vessel and constituted by a stator equipped witha stator winding and a rotor rotating in the stator, the rotor has asecondary conductor provided around a rotor yoke and a permanent magnetembedded in the rotor yoke, and a thermal protector for cutting off thesupply of current to the electric unit in response to a predeterminedtemperature rise is provided on the outer surface of the hermeticvessel. Therefore, it is possible to cut off the supply of current tothe electric unit if the temperature of the outer surface of thehermetic vessel rises due to the heat generated by the electric unit.Thus, a temperature rise in the hermetic vessel can be restrained, sothat an accident, such as a fire, caused by a temperature rise in thehermetic vessel can be prevented.

[0307] In the hermetic electric compressor in accordance with thepresent invention, the thermal protector is constructed of a thermistorwhose resistance value varies with temperature and a controller thatcontrols the supply of current to the electric unit according to achange in the resistance value of the thermistor. Thus, if, for example,the temperature of the hermetic electric compressor rises and exceeds apreset level, the controller controls the supply of current to theelectric unit to reduce the number of revolutions of the electric unitor cut off the supply of current to the electric unit. With thisarrangement, it is possible to control the current supplied to thestator winding before the hermetic electric compressor is run under anoverload condition and damaged. Thus, since the temperature of theelectric unit can be controlled without the need for interrupting theoperation of the hermetic electric compressor, an inconvenience, such asinadequate cooling, attributable to an interrupted operation of thehermetic electric compressor can be securely avoided. Moreover, atemperature rise in the electric unit can be securely controlled bycontrolling the revolution of the electric unit, enabling the servicelife of the electric unit to be prolonged, with resultant dramaticallyimproved reliability of the hermetic electric compressor.

[0308] In the hermetic electric compressor in accordance with thepresent invention, the thermal protector is constituted by a bimetalswitch, so that the current supplied to the electric unit can be cut offalso if the temperature of the hermetic electric compressor rises. Thisobviates the need for controllably adjusting the electric unit by usingan expensive circuit device, making it possible to effect inexpensiveand secure protection of the hermetic electric compressor from damagecaused by a temperature rise.

[0309] In the hermetic electric compressor in accordance with thepresent invention, the thermal protector is constituted by a thermostatthat opens/closes a contact according to temperature, so that thecurrent supplied to the electric unit can be cut off also if thetemperature of the hermetic electric compressor rises. This obviates theneed for controllably adjusting the electric unit by using an expensivecircuit device, making it possible to effect inexpensive and secureprotection of the hermetic electric compressor from damage caused by atemperature rise.

[0310] According to a further aspect of the present invention, thehermetic electric compressor includes a compression unit and an electricunit for driving the compression unit in a hermetic vessel, wherein theelectric unit is secured to the hermetic vessel and constituted by astator equipped with a stator winding and a rotor rotating in thestator, the rotor has a secondary conductor provided around a rotor yokeand a permanent magnet embedded in the rotor yoke, and an overloadprotector for cutting off the supply of current to the electric unit ata predetermined overload current is provided. Therefore, it is possibleto cut off the supply of current to the electric unit if the hermeticelectric compressor is overloaded during operation, thereby allowing theelectric unit to be protected from a temperature rise. Thus, damage tothe electric unit can be prevented, enabling the service life of theelectric unit to be considerably prolonged, with resultant dramaticallyimproved reliability of the hermetic electric compressor.

[0311] In the hermetic electric compressor in accordance with thepresent invention, the overload protector is constituted by an overloadswitch, so that the current supplied to the electric unit can be cut offto prevent a temperature rise in the electric unit thereby to protect itif the hermetic electric compressor is overloaded during operation.Thus, damage to the electric unit can be prevented, enabling the servicelife of the electric unit to be considerably prolonged, with resultantdramatically improved reliability of the hermetic electric compressor.

[0312] In the hermetic electric compressor in accordance with thepresent invention, the overload protector is constituted by a currenttransformer for detecting the current supplied to the electric unit anda controller for controlling the supply of current to the electric uniton the basis of an output of the current transformer, so that thecurrent supplied to the electric unit can be cut off by the controllerif the hermetic electric compressor is overloaded during operation. Thisarrangement makes it possible to prevent a temperature rise in theelectric unit so as to protect the electric unit. Hence, damage to theelectric unit attributable to an overload current can be securelyprevented.

[0313] In the hermetic electric compressor in accordance with thepresent invention, the controller cuts off the supply of current to theelectric unit after a predetermined time elapses since a temperature orcurrent exceeded a predetermined value. It is therefore possible toprotect, by the controller, the electric unit which would be damaged ifcontinuously subjected to an excessive temperature rise or overcurrentcaused by an overload operation or the like of the hermetic electriccompressor. Thus, damage to the electric unit can be prevented, enablingthe service life of the electric unit to be considerably prolonged, withresultant dramatically improved reliability of the hermetic electriccompressor.

[0314] In the hermetic electric compressor in accordance with thepresent invention, the controller restarts the supply of current to theelectric unit after waiting for the elapse of a predetermined delay timesince the supply of current to the electric unit was cut off. This meansthat the delay time is always allowed before the supply of current tothe electric unit is resumed after the supply of current to the electricunit was cut off. It is therefore possible to prevent the rotor frombecoming hot due to, for example, frequent repetition of energizing andde-energizing of the electric unit. Hence, demagnetization of thepermanent magnet embedded in the rotor due to heat can be prevented.

What is claimed is:
 1. A synchronous induction motor comprising: astator equipped with a stator winding; a rotor rotating in the stator; aplurality of secondary conductors which is positioned around a rotoryoke constituting the rotor and which is formed by die casting; endrings which are positioned on the peripheral portions of both endsurfaces of the rotor yoke and which are integrally formed with thesecondary conductors by die casting; a permanent magnet inserted in aslot formed such that it penetrates the rotor yoke; and a pair of endsurface members which is formed of a non-magnetic material and whichcloses the openings of both ends of the slot, wherein one of the endsurface members is secured to the rotor yoke by one of the end ringswhen the secondary conductors and end rings are formed, and the otherend surface member is secured to the rotor yoke by a fixture.
 2. Asynchronous induction motor comprising: a stator equipped with a statorwinding; a rotor rotating in the stator; a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting; end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting; a permanent magnet inserted in a slot formed such that itpenetrates the rotor yoke; and a pair of end surface members whichformed of a non-magnetic material and which closes the openings of bothends of the slot, wherein non-magnetic members are disposed in contactwith the inner sides of the two end rings to secure the two end surfacemembers by pressing them against the rotor yoke by the non-magneticmembers.
 3. A synchronous induction motor comprising: a stator equippedwith a stator winding; a rotor rotating in the stator; a plurality ofsecondary conductors which is positioned around a rotor yokeconstituting the rotor and which is formed by die casting; end ringswhich are positioned on the peripheral portions of both end surfaces ofthe rotor yoke and which are integrally formed with the secondaryconductors by die casting; a permanent magnet inserted in a slot formedsuch that it penetrates the rotor yoke; and a pair of end surfacemembers which is formed of a non-magnetic material and which closes theopenings of both ends of the slot, wherein a balancer formed into apredetermined shape beforehand is secured by a fixture to the rotor yoketogether with the end surface member.
 4. A synchronous induction motorcomprising: a stator equipped with a stator winding; a rotor rotating inthe stator; a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting; end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting; a permanent magnet inserted ina slot formed such that it penetrates the rotor yoke; and a pair of endsurface members which is formed of a non-magnetic material and whichcloses the openings of both ends of the slot, wherein a plurality oflaminated sheet balancers is secured by a fixture to the rotor yoketogether with the end surface member.
 5. A synchronous induction motorcomprising: a stator equipped with a stator winding; a rotor rotating inthe stator; a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting; end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting; a permanent magnet inserted ina slot formed such that it penetrates the rotor yoke; and a pair of endsurface members which is formed of a non-magnetic material and whichcloses the openings of both ends of the slot, wherein at least one ofthe end surface members and a balancer are formed into one piece.
 6. Asynchronous induction motor comprising: a stator equipped with a statorwinding; a rotor rotating in the stator; a plurality of secondaryconductors which is positioned around a rotor yoke constituting therotor and which is formed by die casting; end rings which are positionedon the peripheral portions of both end surfaces of the rotor yoke andwhich are integrally formed with the secondary conductors by diecasting; a permanent magnet inserted in a slot formed such that itpenetrates the rotor yoke; a pair of end surface members which is formedof a non-magnetic material and which closes the openings of both ends ofthe slots; and a balancer secured by being press-fitted to the innerside of at least one of the end rings.
 7. A synchronous induction motorcomprising: a stator equipped with a stator winding; a rotor rotating inthe stator; a plurality of secondary conductors which is positionedaround a rotor yoke constituting the rotor and which is formed by diecasting; end rings which are positioned on the peripheral portions ofboth end surfaces of the rotor yoke and which are integrally formed withthe secondary conductors by die casting; a permanent magnet inserted ina slot formed such that it penetrates the rotor yoke; and a pair of endsurface members which is formed of a non-magnetic material and whichcloses the openings of both ends of the slot in which the permanentmagnet has been inserted, wherein the two end surface members aresecured to the rotor yoke by the two end rings when the secondaryconductors and the end rings are formed.
 8. A synchronous inductionmotor comprising: a stator equipped with a stator winding; a rotor whichis secured to a rotating shaft and which rotates in the stator; asecondary conductor provided around the rotor yoke constituting therotor; and a permanent magnet embedded in the rotor yoke, wherein amagnetic field produced by the permanent magnet does not pass throughthe rotating shaft.
 9. A synchronous induction motor comprising: astator equipped with a stator winding; a rotor which is secured to arotating shaft and which rotates in the stator; a secondary conductorprovided around the rotor yoke constituting the rotor; and a permanentmagnet embedded in the rotor yoke, wherein a magnetic field produced bythe permanent magnet bypasses the rotating shaft.
 10. A synchronousinduction motor comprising: a stator equipped with a stator winding; arotor which is secured to a rotating shaft and which rotates in thestator; a secondary conductor provided around the rotor yokeconstituting the rotor; and a permanent magnet embedded in the rotoryoke, wherein a magnetic field produced by the permanent magnet passesthrough only the rotor yoke, excluding the rotating shaft.
 11. Thesynchronous induction motor according to claim 8, claim 9, or claim 10,wherein a void is formed in the rotor yoke between the permanent magnetand the rotating shaft.
 12. The synchronous induction motor according toclaim 8, claim 9, claim 10, or claim 11, wherein a pair of the permanentmagnets is disposed, sandwiching the rotating shaft therebetween, andpermanent magnets for attracting the magnetic field produced by thepaired permanent magnets are further disposed at both ends of a linethat passes the paired permanent magnets and the rotating shaft.
 13. Thesynchronous induction motor according to claim 8, claim 9, claim 10, orclaim 11, wherein the permanent magnets are provided at both ends of aline that connects two magnetic poles, and the permanent magnets areradially disposed substantially about the rotating shaft.
 14. Asynchronous induction motor comprising: a stator equipped with a statorwinding; a rotor rotating in the stator; a secondary conductor providedaround the rotor yoke constituting the rotor; and a permanent magnetembedded in the rotor yoke, wherein the permanent magnet is magnetizedby current passed through the stator winding.
 15. The synchronousinduction motor according to claim 14, wherein the permanent magnet ismade of a rare earth type magnet or a ferrite magnet.
 16. Thesynchronous induction motor according to claim 14 or claim 15, whereinthe stator winding is of a single-phase configuration and has a primarywinding and an auxiliary winding, and the permanent magnet is magnetizedby the current passed through either the primary winding or theauxiliary winding.
 17. The synchronous induction motor according toclaim 14 or claim 15, wherein the stator winding is of a three-phaseconfiguration that includes a three-phase winding, and the permanentmagnet is magnetized by current passed through a single phase, twophases, or three phases of the stator windings.
 18. The synchronousinduction motor according to claim 14, claim 15, claim 16, or claim 17,wherein the stator winding is coated with varnish or a sticking agentthat is heated to fuse the winding.
 19. The synchronous induction motoraccording to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim7, claim 8, claim 9, claim 10, claim 11, claim 12, claim 13, claim 14,claim 15, claim 16, claim 17, or claim 18, which is installed in acompressor.
 20. The synchronous induction motor according to claim 19,wherein the compressor is used with an air conditioner or an electricrefrigerator or the like.
 21. A manufacturing method for a synchronousinduction motor that has a stator equipped with a stator winding, arotor rotating in the stator, a secondary conductor provided around arotor yoke constituting the rotor, and a permanent magnet embedded inthe rotor yoke, the manufacturing method comprising: a step forembedding a magnet constituent for the permanent magnet in the rotoryoke; and a step for passing current through the stator winding tomagnetize the magnet constituent.
 22. The manufacturing method for thesynchronous induction motor according to claim 21, wherein a rare earthtype or ferrite material is used for the magnet constituent.
 23. Themanufacturing method for the synchronous induction motor according toclaim 21 or claim 22, wherein the stator winding is of a single-phaseconfiguration and has a primary winding an auxiliary winding, and thepermanent magnet is magnetized by the current passed through either theprimary winding or the auxiliary winding.
 24. The manufacturing methodfor the synchronous induction motor according to claim 21 or claim 22,wherein the stator winding is of a three-phase configuration thatincludes a three-phase winding, and the permanent magnet is magnetizedby current passed through a single phase, two phases, or three phases ofthe stator windings.
 25. The manufacturing method for the synchronousinduction motor according to claim 21, claim 22, claim 23, or claim 24,wherein the stator winding is coated with varnish or a sticking agentthat is heated to fuse the windings.
 26. In a synchronous inductionmotor comprising: a stator equipped with a stator winding constructed ofa primary winding and an auxiliary winding; a rotor rotating in thestator; a secondary conductor provided around a rotor yoke constitutingthe rotor; and a permanent magnet embedded in the rotor yoke, a driveunit for the synchronous induction motor, comprising: an operatingcapacitor connected to the auxiliary winding; and a series circuit of astart-up capacitor and a PTC, which is connected in parallel to theoperating capacitor.
 27. In a synchronous induction motor comprising: astator equipped with a stator winding formed of a primary winding and anauxiliary winding; a rotor rotating in the stator; a secondary conductorprovided around a rotor yoke constituting the rotor; and a permanentmagnet embedded in the rotor yoke, a drive unit for the synchronousinduction motor, comprising: an operating capacitor connected to theauxiliary winding; and a PTC connected in parallel to the operatingcapacitor.
 28. In a synchronous induction motor comprising: a statorequipped with a stator winding formed of a primary winding and anauxiliary winding; a rotor rotating in the stator; a secondary conductorprovided around a rotor yoke constituting the rotor; and a permanentmagnet embedded in the rotor yoke, a drive unit for the synchronousinduction motor, comprising: an operating capacitor connected to theauxiliary winding; and a series circuit of a start-up capacitor and astart-up relay contact, which is connected in parallel to the operatingcapacitor.
 29. In a synchronous induction motor comprising: a statorequipped with a stator winding formed of a primary winding and anauxiliary winding; a rotor rotating in the stator; a secondary conductorprovided around a rotor yoke constituting the rotor; and a permanentmagnet embedded in the rotor yoke, a drive unit for the synchronousinduction motor, comprising: an operating capacitor connected to theauxiliary winding.
 30. A hermetic electric compressor comprising acompression unit and an electric unit for driving the compression unitin a hermetic vessel, wherein the electric unit is secured to thehermetic vessel and constituted by a stator equipped with a statorwinding and a rotor rotating in the stator, the rotor comprises asecondary conductor provided around a rotor yoke and a permanent magnetembedded in the rotor yoke, and a thermal protecting means for cuttingoff the supply of current to the electric unit in response to apredetermined temperature rise is provided in the hermetic vessel. 31.The hermetic electric compressor according to claim 30, wherein thethermal protecting means is installed on the stator winding.
 32. Ahermetic electric compressor comprising a compression unit and anelectric unit for driving the compression unit in a hermetic vessel,wherein the electric unit is secured to the hermetic vessel andconstituted by a stator equipped with a stator winding and a rotorrotating in the stator, the rotor comprises a secondary conductorprovided around a rotor yoke and a permanent magnet embedded in therotor yoke, and a thermal protecting means for cutting off the supply ofcurrent to the electric unit in response to a predetermined temperaturerise is provided on the outer surface of the hermetic vessel.
 33. Thehermetic electric compressor according to claim 30, claim 31, or claim32, wherein the thermal protecting means is constructed of a thermistorwhose resistance value varies with temperature and a controller thatcontrols the supply of current to the electric unit according to achange in the resistance value of the thermistor.
 34. The hermeticelectric compressor according to claim 30, claim 31, or claim 32,wherein the thermal protecting means is constructed of a bimetal switch.35. The hermetic electric compressor according to claim 30, claim 31, orclaim 32, wherein the thermal protecting means is constructed of athermostat that opens/closes a contact according to temperature.
 36. Ahermetic electric compressor comprising a compression unit and anelectric unit for driving the compression unit in a hermetic vessel,wherein the electric unit is secured to the hermetic vessel andconstituted by a stator equipped with a stator winding and a rotorrotating in the stator, the rotor comprises a secondary conductorprovided around a rotor yoke and a permanent magnet embedded in therotor yoke, and a thermal protecting means for cutting off the supply ofcurrent to the electric unit at a predetermined overload current isprovided.
 37. The hermetic electric compressor according to claim 36,wherein the overload protecting means is constituted by an overloadswitch.
 38. The hermetic electric compressor according to claim 36,wherein the overload protecting means is constituted by a currenttransformer for detecting the current supplied to the electric unit anda controller for controlling the supply of current to the electric uniton the basis of an output of the current transformer.
 39. The hermeticelectric compressor according to claim 33 or claim 38, wherein thecontroller cuts off the supply of current to the electric unit after apredetermined time elapses since a temperature or current exceeded apredetermined value.
 40. The hermetic electric compressor according toclaim 39, wherein the controller restarts the supply of current to theelectric unit after waiting for the elapse of a predetermined delay timesince the supply of current to the electric unit was cut off.